glmark2 should use standard gnu_dirs waf module

Thanks for looking into this. To request a merge you can go to: https://code.launchpad.net/~vapier/glmark2/glmark2 and click "Propose for merging" (into trunk). This will start the review process.

Regarding the patch, one problem I see is that supporting just --datadir removes the ability to use arbitrary paths as data paths, which is useful for development. For example, a common workflow for developing glmark2 is to build and run in-tree (without installing) by using --data-path=$(pwd)/data . However, this doesn't work as the code forces the 'glmark2' prefix to all data paths.

One idea is to also keep --data-path (explicit data path) and make it override --datadir (GNU datadir). Another idea is to check if --datadir points to a path that already contains glmark2 data, and if so, not append 'glmark2'. I think I prefer the former, as the latter breaks some assumptions about how GNU datadir works.

Please start the review process (as described in the beginning) and we can continue the discussion there.

Applied in trunk rev. 243. I changed your patch slightly to also keep --data-path as a way to specify arbitrary data paths, a feature useful for development. Thanks!