- Strip extra whitespace in regexp answers.  This has a small risk
of changing the meaning of patterns, but it results in cleaner
expressions.

- Convert tabs to spaces.  Students can paste tabs into the editor
and they should be treated as spaces.

- Add parens around patterns so that expressions like "A|B" work
correctly.

The documentation doesn't specify what to do when not automarking,
so I made some guesses on what to return.  Will fix later if needed.

Answer '*' or '.*' is treated as a special case and matches after
all other answers.  This can be used to assign a special score and feedback
to responses that don't match any known pattern so that they can be graded
manually.

There are only needed for the demo authoring page.