Fix handling of $(inherited): Renamed EscapeXCodeArgument to
EscapeXCodeDefine, changed escaping method for spaces, added test.

BUG=gyp:257
TEST=Run small tests on Mac. Also build a xcode project with a gyp file
containing $(inherited) in its 'defines' section, e.g.
----main.cc:
#include <stdio.h>

int main(int argc, char **argv) {
  printf("Hello, world!\n");
  return 0;
}
----main.gyp:
{
  'targets': [
    {
      'target_name': 'main',
      'type': 'executable',
      'mac_bundle': 1,
      'defines': [
        'TRY_QUOTE=with space',
        '$(inherited)',
      ],
      'sources': [ 'main.cc' ],
    }
  ],
}

Patch by Jan Svarovsky <honza@google.com>


git-svn-id: http://gyp.googlecode.com/svn/trunk@1658 78cadc50-ecff-11dd-a971-7dbc132099af