Gripe if some <slot,function> tuple is specified more than once instead of
silently overwriting the previous assignment.

Gripe if the emulation is not recognized instead of silently ignoring the
emulated device.

If an error is detected by pci_parse_slot() then exit from the command line
parsing loop in main().

Submitted by (initial version):	Chris Torek (chris.torek@gmail.com)