Check for circular dependencies between .gyp files....

Check for circular dependencies between .gyp files.

Re-commit r782 backed out at r783.

This check can be disabled with the transitional --no-circular-check
command-line option.  This command-line option should only be used if needed.
When all of Chromium's .gyp files are fixed, the option will be removed, and
there will be no way to bypass this check.

BUG=110
TEST=None yet

Committed: http://code.google.com/p/gyp/source/detail?r=785

[TVL, 2010-02-16 19:52:00]

cl description uses '_' in the options, but code seems to use '-'.

when rolling this in, I guess you'll make the chromium hook add the arg on non
windows platforms?

lgtm otherwise.