<rdar://problem/12362092>

The decorators @expectedFailure (plain and special-case like i386, clang, ...) are modified to optionally take a bugnumber argument
If such an argument is specified, the failure report (or unexpected success report) will include the information passed in as part of the message
This is mostly useful for associating failures to issue IDs in issue management systems (e.g. the LLVM bugzilla)

llvm-svn: 175942