Rename PQsslAttributes() to PQsslAttributeNames(), and const-ify fully.

Per discussion, the original name was a bit misleading, and
PQsslAttributeNames() seems more apropos.  It's not quite too late to
change this in 9.5, so let's change it while we can.

Also, make sure that the pointer array is const, not only the pointed-to
strings.

Minor documentation wordsmithing while at it.

Lars Kanis, slight adjustments by me

doc/src/sgml/libpq.sgml

@@ -1873,7 +1873,7 @@ int PQsslInUse(const PGconn *conn);
      </listitem>
     </varlistentry>
 
-    <varlistentry id="libpq-pqsslAttribute">
+    <varlistentry id="libpq-pqsslattribute">
      <term><function>PQsslAttribute</function><indexterm><primary>PQsslAttribute</></></term>
      <listitem>
       <para>
@@ -1947,13 +1947,13 @@ const char *PQsslAttribute(const PGconn *conn, const char *attribute_name);
      </listitem>
     </varlistentry>
 
-    <varlistentry id="libpq-pqsslattributes">
-     <term><function>PQsslAttributes</function><indexterm><primary>PQsslAttributes</></></term>
+    <varlistentry id="libpq-pqsslattributenames">
+     <term><function>PQsslAttributeNames</function><indexterm><primary>PQsslAttributeNames</></></term>
      <listitem>
       <para>
        Return an array of SSL attribute names available. The array is terminated by a NULL pointer.
 <synopsis>
-const char **PQsslAttributes(const PGconn *conn);
+const char * const * PQsslAttributeNames(const PGconn *conn);
 </synopsis>
       </para>
      </listitem>
@@ -1963,15 +1963,15 @@ const char **PQsslAttributes(const PGconn *conn);
      <term><function>PQsslStruct</function><indexterm><primary>PQsslStruct</></></term>
      <listitem>
       <para>
-       Return a pointer to an SSL-implementation specific object describing
+       Return a pointer to an SSL-implementation-specific object describing
        the connection.
 <synopsis>
 void *PQsslStruct(const PGconn *conn, const char *struct_name);
 </synopsis>
       </para>
       <para>
-       The structs available depends on the SSL implementation in use.
-       For OpenSSL, there is one struct, under the name "OpenSSL",
+       The struct(s) available depend on the SSL implementation in use.
+       For OpenSSL, there is one struct, available under the name "OpenSSL",
        and it returns a pointer to the OpenSSL <literal>SSL</literal> struct.
        To use this function, code along the following lines could be used:
 <programlisting><![CDATA[

doc/src/sgml/release-9.5.sgml

@@ -608,18 +608,22 @@ FIXME: Add Andres
 2015-02-03 [91fa7b4] Heikki..: Add API functions to libpq to interrogate SSL ..
 -->
        <para>
-        Add <application>libpq</> function <link
-        linkend="libpq-pqsslAttribute"><function>PQsslAttribute()</></>
-        that returns <acronym>SSL</> information (Heikki Linnakangas)
+        Add <application>libpq</> functions to return <acronym>SSL</>
+        information in an implementation-independent way (Heikki Linnakangas)
        </para>
 
        <para>
-        While <link linkend="libpq-pqgetssl"><function>PQgetssl()</></>
-        can still be used to call <productname>OpenSSL</>
-        functions, <function>PQsslAttribute()</> returns <acronym>SSL</>
-        information in an <acronym>SSL</>-implementation-independent way.
-        (Future versions of libpq might support other <acronym>SSL</>
-        implementations.)
+        While <link linkend="libpq-pqgetssl"><function>PQgetssl()</></> can
+        still be used to call <productname>OpenSSL</> functions, it is now
+        considered deprecated because future versions
+        of <application>libpq</> might support other <acronym>SSL</>
+        implementations.  When possible, use the new
+        functions <link
+        linkend="libpq-pqsslattribute"><function>PQsslAttribute()</></>, <link
+        linkend="libpq-pqsslattributenames"><function>PQsslAttributeNames()</></>,
+        and <link linkend="libpq-pqsslinuse"><function>PQsslInUse()</></>
+        to obtain <acronym>SSL</> information in
+        an <acronym>SSL</>-implementation-independent way.
        </para>
       </listitem>
 

src/interfaces/libpq/exports.txt

@@ -167,6 +167,6 @@ lo_truncate64             164
 PQconninfo                165
 PQsslInUse                166
 PQsslStruct               167
-PQsslAttributes           168
+PQsslAttributeNames       168
 PQsslAttribute            169
 PQsetErrorContextVisibility 170

src/interfaces/libpq/fe-secure-openssl.c

@@ -1532,10 +1532,10 @@ PQsslStruct(PGconn *conn, const char *struct_name)
 	return NULL;
 }
 
-const char **
-PQsslAttributes(PGconn *conn)
+const char *const *
+PQsslAttributeNames(PGconn *conn)
 {
-	static const char *result[] = {
+	static const char *const result[] = {
 		"library",
 		"key_bits",
 		"cipher",

src/interfaces/libpq/fe-secure.c

@@ -408,10 +408,10 @@ PQsslAttribute(PGconn *conn, const char *attribute_name)
 	return NULL;
 }
 
-const char **
-PQsslAttributes(PGconn *conn)
+const char *const *
+PQsslAttributeNames(PGconn *conn)
 {
-	static const char *result[] = {NULL};
+	static const char *const result[] = {NULL};
 
 	return result;
 }

src/interfaces/libpq/libpq-fe.h

@@ -329,7 +329,7 @@ extern int	PQsetClientEncoding(PGconn *conn, const char *encoding);
 extern int	PQsslInUse(PGconn *conn);
 extern void *PQsslStruct(PGconn *conn, const char *struct_name);
 extern const char *PQsslAttribute(PGconn *conn, const char *attribute_name);
-extern const char **PQsslAttributes(PGconn *conn);
+extern const char *const * PQsslAttributeNames(PGconn *conn);
 
 /* Get the OpenSSL structure associated with a connection. Returns NULL for
  * unencrypted connections or if any other TLS library is in use. */