* scheduled snapshots at the same time often step on each other, causing
  one or both to fail, or to produce the wrong error messages if they
  would have failed anyway. (monthly default TOD is 22:05 for all sources)

* remove_source fails if the source fileset has been removed by hand
  already.  it should at least remove the config file entries for
  that source.

* detect and clean up partial (failed) send's to backup host

* need to categorize snapsched commands into root commands, required by
  the `scheduled` snapshot program and by admin commands that should/need
  to be run by root, and user commands like diff and get.  some kind of
  priviledge drop needs to be done for those commands, but the mount
  part must be done by a priviledged program, so that needs to be figured
  out.  sudo is not an option, because it isn't installed or used on
  all systems.  perhaps autofs can be used to mount SNAP_MOUNT_DIR
  or something.  we are considering autofs for another feature as well.

* `get' :	should take a second argument for the destination of a
			file, as well as the interval argument!
		:	installs the file as owned by root, when it should retain
			all the original ownership and permissions
