Merge pull request #51 from goehle/bugfixes

Merging your fixes.  (As a practice, I'd like to see a separate pull for each bug, rather than mixing them together.  That makes it clearer which changes are for which bug, and makes it easier to back out of changes if there ends up being a problem.  Here, the fixes for dollar signs are mixed in with the fixes for the printing of hints.)
Update PGessaymacros.pl

Roll back HTML::Scubber a bit to allow <'s
Backport pull request #54 (allow errors from adaptive parameters to appear in the message area)
Merge pull request #58 from dpvc/hotfix/2.7-FormulaUpToConstant

Backport pull request #54 as a hotfix to v2.7
Merge branch 'master' of http://github.com/openwebwork/pg into bugfixes

Conflicts:
	macros/PGessaymacros.pl