GitHub plugin: fix threading issues when libcurl is build against openssl.

* Dick Hollenbeck also contributed commit r6440.  I inadvertently forgot to set
  the Bazaar author tag before I committed it.  My apologies.
* Switch to static linking of libcurl and on linux and windows and also
  statically link in only required portions of openssl.
* Add the required thread locks which openssl needs.
* Remove the get curl version call from BASEFRAME since it pulls in curl and
  openssl into every derived wxFrame class link image.
* Remove curl function from PGM_BASE, switch to atexit() instead.  Anything in
  PGM_BASE made the singletops bigger.
* Tested on Linux, Windows, and OSX.

common/basicframe.cpp

@@ -28,7 +28,6 @@
  * @brief EDA_BASE_FRAME class implementation.
  */
 
-#include <kicad_curl/kicad_curl.h> /* Include before any wx file */
 #include <wx/aboutdlg.h>
 #include <wx/fontdlg.h>
 #include <wx/clipbrd.h>
@@ -573,8 +572,6 @@ void EDA_BASE_FRAME::CopyVersionInfoToClipboard( wxCommandEvent&  event )
                 << ( BOOST_VERSION / 100 % 1000 ) << wxT( "." )
                 << ( BOOST_VERSION % 100 ) << wxT( "\n" );
 
-    msg_version <<  KICAD_CURL::GetSimpleVersion() << wxT( "\n" );
-
     msg_version << wxT( "         USE_WX_GRAPHICS_CONTEXT=" );
 #ifdef USE_WX_GRAPHICS_CONTEXT
     msg_version << wxT( "ON\n" );