[krbdev.mit.edu #8806] kdb5_util errors on command arguments matching command names

kdb5_util's top-level argv loop continues parsing command-line 
arguments after it finds the command name.  This is probably 
intentional, so that global options like "-r realm" can appear before 
or after the command name.  However, if any of the command arguments 
happen to match a command name, usage() is called with no explanation.

I ran into this when running trying to load a dump file named "dump" 
with "kdb5_util load dump".