flexbackup

I implemented lzma compression in the flexbackup script. LZMA is an open
source, non-patent-encumbered compressor that compresses around 15% better
than bzip2 though it is more time consuming. This is also the compression
algorithm in popular 7zip, but p7zip didn't support both stdin and stdout
piping in the same command, so I resorted to lzma.

Currently it does not allow specifying any compression levels but defaults
to the maximum, which IMO is the optimum behavior. LZMA supports two levels
of compression: 0 and 1. 0 compresses almost identically to bzip2 and 1
compresses better and slower.

Please consider inclusion in flexbackup

(I didn't implement log compression in lzma, because I couldn't see the
point of being so compression-greedy with a tiny logfile... :D)