Update ninja_syntax.py from upstream.

This is ninja_syntax.py as of ninja commit
368f5bc64ddd2dcea2662d6c932157314be3e09b . It's newer than the latest
ninja release because I want to provide an opt-in flag for the "deps"
feature, which isn't in a ninja release yet.

TBR=scottmg
Review URL: https://codereview.chromium.org/13915013

git-svn-id: http://gyp.googlecode.com/svn/trunk@1609 78cadc50-ecff-11dd-a971-7dbc132099af