Update ninja to v120715

On both mac and linux, I ran:

git checkout release-120715
ninja
./ninja ninja_test
./ninja_test  # all passed
strip ninja

Changes since the last push:
* ninja now has a functional -V flag that prints version information
* ninja is a lot faster. On my MBP, empty builds go from 1.8s to 1.1s,
  on my linux box from 1.4s to 0.9s
* ninja now has a -l N flag to do parallelsim based on load average

On linux, the binary grew 24 bytes, from 129920 to 129944. I used
gcc 4.4.3 to build ninja.

On mac, it grew from 4200 byte from 120904 to 125104 (likely caused by me
using a newer clang). I used clang r159409 to build ninja.

TBR=maruel@chromium.org

Review URL: https://chromiumcodereview.appspot.com/10810025

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@147557 0039d316-1c4b-4281-b951-d872f2087c98