Fixes bug 7512.

while supporting older rsyncs that send dev == 0.

Based on a patch by Matt, but further tweaked to deal with -q=foo.

Ultimately this should be upstreamed, but for now lets get this
functionality into rsync.

(Tweaked by Wayne to follow his preferred style.)

Rsync was showing the full destination path, which was confusing because
nothing is created at that path and was especially bogus in combination
with the source name of a solo file.

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=506830

because it is static.

It took me long enough to realize this that I think it is worth
documenting.

improve that of --inplace while I'm at it.

Originally explained at:

http://lists.samba.org/archive/rsync/2006-February/014838.html

- The receiver now sends keep-alive messages to the generator
  when it is actively doing work and hasn't sent anything
  recently.  This ensures that the generator won't timeout
  if the receiver is working hard.
- The perform_io() code has improved keep-alive participation.
- Allow the sender to send some keep-alive messages, which
  ensures that if it is in a lull, it can probe the socket.

the git-status checking into a library.