add some mimetype for geometry shaders

This gives at least some syntax highlighting.
(cherry picked from commit 04c5425d)

Change-Id: I04c5425de2292c9da66c7c1dd2ae0c646528ca07x
Reviewed-on: http://codereview.qt.nokia.com/390


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: hjk <qthjk@ovi.com>