Remove libsvn_auth_gpg_agent and move gpg-agent support into libsvn_subr.
There is no need to put gpg-agent support into a library loaded at runtime. The svn code talks to the GPG agent via a UNIX stream socket. There are no massive external library dependencies involved that we need to keep at a distance, as with GNOME or KDE.
This should also fix the problem where svn fails to enable gpg-agent support on Mac OS X because of a filename mismatch (*.so vs. *.dylib).
* subversion/include/svn_auth.h (svn_auth_gpg_agent_version): Remove declaration. A version function is only needed for DSOs. (svn_auth_get_gpg_agent_simple_provider): Declare this function on Darwin. Remove mention of libsvn_auth_gpg_agent from docstring.
* subversion/libsvn_auth_gpg_agent/gpg_agent.c: Move to ...
* subversion/libsvn_subr/gpg_agent.c: ... here. Wrap all code into the SVN_HAVE_GPG_AGENT define.
* subversion/libsvn_subr/auth.c (svn_auth_get_platform_specific_provider): Directly call svn_auth_get_gpg_agent_simple_provider() if SVN_HAVE_GPG_AGENT is defined instead of loading gpg-agent support as a DSO.