Use a QMap instead of a QHash for the regexp flags

This is unit-tested, so we need a predictable order. Therefore, we
can't use QHash anymore. Besides, this is just for 4 elements, so
there shouldn't be a perceptible overhead.

Change-Id: I878f77982e8070f3bc30bd2458e26e61b22f313d
Reviewed-by: Giuseppe D'Angelo <dangelog@gmail.com>
Reviewed-by: Toby Tomkins <toby.tomkins@nokia.com>