is_folder_selected(), get_tree_path_filename() and separate menu
item callbacks.
Rename "Open with..." popup item "Open externally" ("..." is usually
used when the user can input more information).
git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@2133 ea778897-0a13-0410-b9d1-a72fbfd435f5