`make-regexp-tweaker', which produces a regexp that cannot match an
empty string at the beginning or the end of the input. This:
* simplies a whole bunch of messy and fragile code
* makes `regexp-split' and friends usable with a pattern like #px"\\b"
(which previously would match in every position, making it explode
the string to 1-character strings)
* makes it even closer to what perl does, the only way that we produce
a different result from perl now is that we don't blindly drop empty
matches at the end like perl (it *does* keep empty matches in the
beginning though)
The two tests that demonstrated the difference are now changed, and a
bunch of other tests added.
svn: r12575
* Split string.ss into string-mzlib.ss which is left in mzlib.ss
* Call the string.ss from scheme (which now has only stuff from scheme/base)
svn: r9196
