Update benchmark.py

wasn't working with locals(), so changed to globals(), which according to the docs, "always the dictionary of the current module" [1], which was the intended behavior in the first place, I think.

[1]http://docs.python.org/2/library/functions.html#globals
Merge branch 'master' of github.com:aspidites/kivy
Merge pull request #1868 from aspidites/master

get benchmarks running again