gsdx ogl: automatic setup of geometry shader

* disable it for gallium Mesa driver
* Re-enable it for Nvidia driver
gsdx-ogl: restore gles build

Add the --gles build option to the linux main script
Ifdef all gl code not supported on gles3 (note some will be reenabled for gles3.1)

Note: it probably doesn't run anymore. My Nvidia driver doesn't support
yet egl/gles so I can't test it. Feel free to contribute.
cmake: fatal error when path contains some parenthesis
cmake: sed /PROJECT_SOURCE_DIR/CMAKE_SOURCE_DIR/

The former depends on the project command. Whereas the latter is the true absolute path
of the project
Fix segfault in non-dev build by adding extra check for NULL.
Fix out of tree build.

Tell git to look in the source dir for the repository.