Storage compression patch for Rsync (unfinished)

[Craig Barratt]

> Block checksums come from the receiver so cached block
> checksums are only useful when sending to a server which had
> better know it has block checksums cached.

The first statement is true (block checksums come from the receiver),
but the second doesn't follow.  I need to cover the case where the
client is the receiver and the client is caching the checksums. That
needs a command-line switch, since the server would otherwise use
time(NULL) as the checksum seed, which is then sent from the server
to the client at protocol startup.

I agree with your changes though: the command-line handling code can set
checksum_seed if any of write-batch, read-batch, or fixed-checksum-seed
are specified, avoiding the additional variable.

Craig