Fix for empty default variables used as paths.

With r1637 default varaibles used as paths are now being relativized.
However, if the default variable used as a path is empty, gyp throws an error.

R=mark@chromium.org

Review URL: https://codereview.chromium.org/15968005

git-svn-id: http://gyp.googlecode.com/svn/trunk@1638 78cadc50-ecff-11dd-a971-7dbc132099af
Fix test/variables/commands/update_golden. 

Without this fix, 

cd test/variables/commands && ./update_golden && cd - && \ 
./gyptest.py test/variables/commands 

led to failing tests. Now it works.
TBR=scottmg

Review URL: https://codereview.chromium.org/16047006

git-svn-id: http://gyp.googlecode.com/svn/trunk@1639 78cadc50-ecff-11dd-a971-7dbc132099af
Revert r1637, it broke gyp for chromium (due to use_titlecase_in_grd_files in
build/common.gypi).

Also revert r1638 since it's no longer needed.

Add tests for default variables in gypi files, especially for _files variables,
especially if those are ints (which were broken in chromium) or empty (which
was addressed by r1638).

The golden files were updated by running

   cd test/variables/commands && ./update_golden && cd -

TBR=torne

Review URL: https://codereview.chromium.org/15972007

git-svn-id: http://gyp.googlecode.com/svn/trunk@1640 78cadc50-ecff-11dd-a971-7dbc132099af
ninja: Enable deps mode on non-windows.

Windows will follow soon, if the new 1.3.0.git binary has worked well for a week
or so.

The Opera guys reported issues with deps mode when they tried it
(https://code.google.com/p/chromium/issues/detail?id=245034), but now they can
no longer repro. Maybe their issue was unrelated to deps mode.

Several folks have been using deps mode for a while without issues, so it should
work. If this does break your build somehow, please tell me about it.

No test since this should be no behavior change, it only makes things faster.

BUG=chromium:245034
Review URL: https://codereview.chromium.org/15713018/



git-svn-id: http://gyp.googlecode.com/svn/trunk@1641 78cadc50-ecff-11dd-a971-7dbc132099af