Adding gzip support the dumpscan suite

I recently really started looking at the dumpscan suite from the folks at CMU SCS. It's a fairly useful set of libraries and tools for looking at AFS volume dumps, which has been a fascination of mine for a while.

Both for use at home, where I want to write a utility to merge several volume dumps into one, and at work, where it would be neat to do some sort of cataloging of dumps, this is a windfall, making such tools pretty easy to write. At both places, however, volume dumps tend to be gzipped right after they are created (or even as they are created). The dumpscan suite includes a generic library for file-like objects (called XFILE), that is easily extensible, and after thinking about it for 10 minutes while trying to fall asleep I got out of bed and just added gzip support.

It's completely cargo-cultish, and entirely and utterly untested, but it works enough that I can run afsdump_scan and have it scan directly a gzipped volume dump. Find it here.