Fix passing ActiveSupport::SafeBuffer to param encoders

Simply re-use `Faraday::Utils.escape/unescape` instead of reimplementing
them for each encoder.

lib/faraday/parameters.rb

@@ -1,15 +1,10 @@
+require "forwardable"
+
 module Faraday
   module NestedParamsEncoder
-    ESCAPE_RE = /[^a-zA-Z0-9 .~_-]/
-
-    def self.escape(s)
-      s.to_s.gsub(ESCAPE_RE) {|match|
-        '%' + match.unpack('H2' * match.bytesize).join('%').upcase
-      }.tr(' ', '+')
-    end
-
-    def self.unescape(s)
-      CGI.unescape(s.to_s)
+    class << self
+      extend Forwardable
+      def_delegators :'Faraday::Utils', :escape, :unescape
     end
 
     def self.encode(params)
@@ -117,16 +112,9 @@ module Faraday
   end
 
   module FlatParamsEncoder
-    ESCAPE_RE = /[^a-zA-Z0-9 .~_-]/
-
-    def self.escape(s)
-      return s.to_s.gsub(ESCAPE_RE) {
-        '%' + $&.unpack('H2' * $&.bytesize).join('%').upcase
-      }.tr(' ', '+')
-    end
-
-    def self.unescape(s)
-      CGI.unescape(s.to_s)
+    class << self
+      extend Forwardable
+      def_delegators :'Faraday::Utils', :escape, :unescape
     end
 
     def self.encode(params)

test/parameters_test.rb

@@ -0,0 +1,24 @@
+require File.expand_path("../helper", __FILE__)
+
+class TestParameters < Faraday::TestCase
+  # emulates ActiveSupport::SafeBuffer#gsub
+  FakeSafeBuffer = Struct.new(:string) do
+    def to_s() self end
+    def gsub(regex)
+      string.gsub(regex) {
+        match, = $&, '' =~ /a/
+        yield(match)
+      }
+    end
+  end
+
+  def test_escaping_safe_buffer_nested
+    monies = FakeSafeBuffer.new("$32,000.00")
+    assert_equal "a=%2432%2C000.00", Faraday::NestedParamsEncoder.encode("a" => monies)
+  end
+
+  def test_escaping_safe_buffer_flat
+    monies = FakeSafeBuffer.new("$32,000.00")
+    assert_equal "a=%2432%2C000.00", Faraday::FlatParamsEncoder.encode("a" => monies)
+  end
+end