Patch #59 by Vincent Legoll: Fix clearance typo (forgot to commit)
Patch #59 by Vincent Legoll: use del for dicts, not erase. Also check key existence first, to not fail on deregistration of unregistered objects.
Patch #59 by Vincent Legoll: fix sefl typo
Patch #59 by Vincent Legoll: remove duplicate include
Patch #59 by Vincent Legoll: add missing import of server_lib to computer.py
Patch #59 by Vincent Legoll: fix call to debug.error that had too many arguments for a format string (cut-n-paste error most probably)
Patch #59 by Turbo Beholder: fix typo in unit.py (NSigni*fi*ficant)
Patch #59 by Vincent Legoll: fix varname typo in unit.py (whichshignificant -> whichsignificant)
Patch #59 by Vincent Legoll: fix clearence->clearance typos
Patch #58 by Vincent Legoll: unset mission-relevant flag for done patrol points