• core/gpc_api.php
  (gpc_set_cookie): new function to set a cookie
  Victor is going to update this later to add a checksum
  (gpc_clear_cookie): new function to clear a cookie
• set_project.php: use gpc_api functions for cookies
• config_defaults_inc.php
  ($g_cookie_domain): set to '' by default
  ($g_project_cookie_val): set to '0' by default so we can phase out forcing the user to select a project at login
  I also added a note about what globals we can remove once the conversion to gpc_api is complete

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1507 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9