Merges recent upstream changes from martine/master:
- Adds -d explain for debugging;
- Adds support for NINJA_STATUS to configure output (see ninja manual);
- Other minor fixes.

TBR=maruel@chromium.org
Review URL: https://chromiumcodereview.appspot.com/10235008

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@134119 0039d316-1c4b-4281-b951-d872f2087c98