Add a simple PVS parser for use in subtyping.

The subtypes given in tables are given in PVS syntax.  To use these in other
languages, the TET needs to parse PVS expressions.  Note that this parser
is very basic, and only handles the bare minimum needed.  It only handles
basic Math expressions, similar to Matlab.  It doesn't do /= yet, due to missing
support further down the stack.

git-svn-id: https://groke.mcmaster.ca/svn/grad/colin/branches/TableTool_javization@10850 57e6efec-57d4-0310-aeb1-a6c144bb1a8b