Make _CopyXIBFile() work with Xcode 4.3
Make _CopyXIBFile() work with Xcode 4.3

For now, this will pick /usr/bin/ibtool, but once 91675 is
fixed, it'll do the right thing.

BUG=chromium:117498,chromium:91675
TEST=none
Review URL: https://chromiumcodereview.appspot.com/9646026

csulmone/gyp,csulmone/gyp,csulmone/gyp,csulmone/gyp