the pattern must have a fixed width.
- got rid of array-module dependencies; the match pro-
gram is now stored inside the pattern object, rather
than in an extra string buffer.
- cleaned up a various of potential leaks, api abuses,
and other minors in the engine module.
- use mal's new isalnum macro, rather than my own work-
around.
- untabified test_sre.py. seems like I removed a couple
of trailing spaces in the process...