delete temporary buffer in ofAppGlutWindow

This fixes #2817.
Fix memory leak in ofAppGLFWWindow, catch-up for #2817
Merge pull request #2818 from saki7/ofAppGlutWindow-leak-fix

delete temporary buffer in ofAppGlutWindow
Merge branch 'master' of https://github.com/openframeworks/openFrameworks.git into VS2013