Removed PGL.Context subclass

git-svn-id: http://processing.googlecode.com/svn/trunk@10795 fe3ceab9-de17-3b67-bb2e-7d58edd5e4d6
PGL.getBackTextureName, PGL.getFrontTextureName are protected

git-svn-id: http://processing.googlecode.com/svn/trunk@10796 fe3ceab9-de17-3b67-bb2e-7d58edd5e4d6
PGL.threadIsCurrent() is not static to avoid problems with subclassed renderers

git-svn-id: http://processing.googlecode.com/svn/trunk@10797 fe3ceab9-de17-3b67-bb2e-7d58edd5e4d6
Solving some class visibility issues

git-svn-id: http://processing.googlecode.com/svn/trunk@10798 fe3ceab9-de17-3b67-bb2e-7d58edd5e4d6