Added warning if GLX version is less than 1.3. Pbuffers need GLX 1.3 and the...

Added warning if GLX version is less than 1.3. Pbuffers need GLX 1.3 and the pixmap fallback for 1.2 does not work on all systems.
TEST=try
BUG=none

Review URL: http://codereview.chromium.org/2382002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@48538 0039d316-1c4b-4281-b951-d872f2087c98