[gtk+] (5 commits) Non-fast-forward update to branch wip/ebassi/legacy-gl

[Emmanuele Bassi <ebassi src gnome org>]

The branch 'wip/ebassi/legacy-gl' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  99650ff... gl: Use older GLSL shaders with legacy contexts
  155329c... x11: Create legacy GLX contexts
  8d4b2cb... x11: Control legacy GL context via environment variable
  5189656... Allow testglarea to work with legacy GL contexts

Commits added to the branch:

  3942056... gl: Use older GLSL shaders with legacy contexts
  aeb4ed1... x11: Create legacy GLX contexts
  79049cf... x11: Control legacy GL context via environment variable
  02a585d... Allow testglarea to work with legacy GL contexts
  d1ecb62... docs: Improve description of gdk_gl_context_is_legacy()