Universal Machine implementation as specified by ICFPC '06

I didn't actually participate in that contest, and tinkered with the UM around 2008-2009 to look at a few problems in preparation for ICFPC '09.

This should be fully capable of running sandmark, codex and reference um, as supplied by CMU.

stress.um is a simple hand-coded test intended to bring any implementation with non-CoW pages to its knees. Which it does neatly. Unfortunately, CoW pages are useless in codex usage scenarios.

./um --selftest will run a simple self-test (duh). It requires sandmark.umz that you should obtain elsewhere.