Add the exponent operator.

Add parsing and generating support for the exponent operator.  It currently
doesn't support generation over fixed point values, since CVC3 doesn't include
an easy to use function.

git-svn-id: https://groke.mcmaster.ca/svn/grad/colin/branches/TableTool_javization@10857 57e6efec-57d4-0310-aeb1-a6c144bb1a8b