message threads. This didn't cause any problems with the archive, but
if you extracted the thread in question without reopening the archive
you ended up getting the whole pre-sized buffer instead of just the part
with data in it.
Load the TOC if needed in Nu_ExtractThread.
When thread extraction fails, don't send an update to the progress
updater if there isn't a progress updater.
Generalized compression method enable/disable. Now any method can be
removed. Applications can call NuTestFeature() to figure out what is
supported by the copy of NufxLib they're linked against.
