clean up --sourcedir/--sourcedirectory conflict

clean up --sourcedir/--sourcedirectory conflict

* Move two move command-specific options to only be accepted by the commands
  that use them. The options are:
  --sourcedir, --destdir
* If any third-party debhelper commands use either of the above options,
  they will be broken, and need to be changed to pass options to init().

This was done because of a conflict with the --sourcedirectory options
used by dh_auto_*. I originally wanted to make dh_auto_* and dh_install
both use --sourcedir, but that didn't work out.