implement fuzzy numerical match in processing answers

This patch allows for fuzzy numerical matches in answers to fill in the blank questions. We have a user who is trying to use Sakai in a technical class. That inevitably involves numerical questions. There's no practical way to do this unless you can allow answers in varying formats (e.g. 1000 or 1E3) and with a range of acceptable values (to allow for slightly imprecision of numerical calculations).

The enclosed patch implements a syntax such as %F%100,10 for a value of 100 plus or minus 10. %F% is intended to be expandable to flags for other kinds of answer processing. F is, of course, for floating point.

This is with respect to revision 2090.