Implement support for expiring expected results in validate_failures.py.

Implement support for expiring expected results in validate_failures.py.

I noticed recently that while the validator was accepting the
'expire=YYYYMMDD' attribute, it was not actually doing anything with
it.

This patch fixes the oversight.

2012-08-13  Diego Novillo  <dnovillo@google.com>

	* testsuite-management/validate_failures.py: Import datetime.
	(TestResult.ExpirationDate): New.
	(TestResult.HasExpired): New.
	(ParseSummary): Call it.  If it returns True, warn that the
	expected failure has expired and do not add it to the set of
	expected results.
	(GetResults): Clarify documentation.

From-SVN: r190351