[Bf-codereview] Use cmake install target on Mac (issue4287048)

[brechtvanlommel at gmail.com]

Reviewers: bf-codereview_blender.org,

Description:
Other platforms are already using it, this brings Mac in line.

Will commit in 24 hours if no comments come up.

Please review this at http://codereview.appspot.com/4287048/

Affected files:
   GNUmakefile
   source/creator/CMakeLists.txt