Prevent suggesting wrong command

When we got a totally wrong command (e.g. not a spell error), do not suggest it in spell corretions
Better handling of wrong spelled commands

Commands without alias where not correctly corrected
Better search of svn_operation in command line

But this is not perfect... (see the fixme)
also, do not print "Did you mean one of these?" if no spell correction
Fix "os.execl" when no svn_operation