Fix typo correction of one qualified name to another.

When suggesting "foo::bar" as a correction for "fob::bar" we mistakenly
replaced only "bar" with "foo::bar" producing "fob::foo::bar" which was broken.

This corrects that replacement in as many places as I could find & provides
test cases for all those cases I could find a test case for. There are a couple
that don't seem to be reachable (one looks entirely dead, the other just
doesn't seem to ever get called with a namespace to namespace change).

Review by Richard Smith ( http://llvm-reviews.chandlerc.com/D57 ).

llvm-svn: 165817