Catch an exception in Template Haskell code

		Merge to STABLE

If the code run by a Template Haskell splice fails with, say,
a pattern-match failure, we should not report it as a GHC panic.
It's a bug in the user's program.

This commit fixes up the exception handling to do the right thing.

Fixes SourceForge item #1201666

TH_fail tests it.