#7 Command-line type checking

[Alexander Koller]

Find a way in which the command-line arguments can be
checked for consistency in a clever way. For example,
the --port option only makes sense for the "server"
command. The --output option and the --no-output option
contradict each other and shouldn't be useable in the
same call to utool.

At the moment, contradictory command-line options are
ignored (more or less gracefully).

The consistency check should not be much longer than
the current code for parsing the command-line
arguments. In particular, no code in the switch
statements must be duplicated, because this would be
insanely error-prone.