Code review comment for lp://staging/~jesse-barker/glmark2/extra-support

Looks good.

Some ideas for future consideration (more or less related to this branch):

1. Create a resource path handling class to find resources in the available locations instead of hardcoding paths. For example, vtx_shader_path = Resources::find("shader/desktop.vert").

2. Istead of having a "data path" and an "extras path" support multiple (even more than 2!) "data paths". For example './waf configure --data-path=$(pwd)/data --data-path=$(pwd)/../glmark2-extras'. This would require some work on both the build system side and the glmark2 resource handling side (like the change described in (1)).

3. Allow Model::load() to accept arbitrary paths so that users can load additional models from the filesystem.