Fix gettextutil.Message handling of deep copy failures

Broadened deep copy exception handling and changed the keyword
dictionary deep copy to doing each element separately so that only
the failing dictionary item is converted to unicode.

Also added test cases.

Closes-bug: #1290468
Change-Id: I15f3880b32bec55bb61d96af41762c98486a274d
Merge "Fix gettextutil.Message handling of deep copy failures"