Resume expanding abbreviations for command-line options

The fix for bug 4647 accidentally removed our hack from bug 586 that
rewrote HashedControlPassword to __HashedControlSessionPassword when
it appears on the commandline (which allowed the user to set her own
HashedControlPassword in the torrc file while the controller generates
a fresh session password for each run).

Fixes bug 12948; bugfix on 0.2.5.1-alpha.