Add pylint presubmit check.

Add pylint presubmit check.

All checks that were triggered were disabled in pylintrc. I put two lists, one
of warnings that are worthless and one list with the warnings that should be
enabled in a subsequent change. Since fixing these can be messy, this is left as
an exercise to the reader.

BUG=
TEST=

Committed: http://code.google.com/p/gyp/source/detail?r=1103

[M-A Ruel, 2011-11-28 16:13:52]

In practice, I recommend fixing one warning per CL, it's easier to manage.

[Mark Mentovai, 2011-11-28 16:20:35]

LGTM