Test suite: use regexes to match the compiler error message.

GHC >= 7.7 outputs Unicode quotation characters when possible (see
http://ghc.haskell.org/trac/ghc/ticket/2507 ), which breaks tests that rely on
substring matching.

Alternatively, we can run GHC with 'LC_ALL=C', but I'm not sure whether that'll
work on Windows.