More of same.

More of same.
Actually, it's not quite the same:
-use crc_init(xz_crc32_table,1) -- I guessed on this one based on a match between magic constants, then tested it. First try was wrong, but this works.
(This is the sole difference in terms of actual _code_, as opposed to cleaning up defines and the like--here, it adds 48 bytes to final size if xzcat is the only toy, but drops 32 bytes if bzcat is also enabled...)
-Move some crc64 code to where the comments are. This puts them near the area where they're used.
-Remove some relics of separate files (we had half a dozen "this file is in the public domain" notices, a duplicate include, and used extern declarations for functions in the samefile)