Note that the original implementation failed on sbcl for some reason.
But using a closure to compile the pattern works and the pattern is
only compiled once instead of for every call. See the comments for
more info.
parse_timedate tests pass on sbcl and other lisps.
Use built-in pregexp for sregex routines in stringproc
Since pregexp is now built in to maxima, we can delete the (old) copy
in stringproc. This also means we don't need to load pregexp in
sregex.mac. Finally, since pregexp is in its own Lisp package, we
need to update sregex.lisp to prefix all uses of pregexp with the
package name.
sregex might be a little faster now too since pregexp is compiled.
