If the next available mailbox is not in the free state, print a warning
and handle the condition as a temporary resource shortage. The condition
should never happen, but we shouldn't panic since recovery is possible.
hasseen_isadev so this will be less noisy when conflicts do exist.
Also eliminate redundant warnings about conflicts.
Requested by: bde
Reviewed by: gibbs
o For bt and aha only probe the one I/O range if a specific I/O is specified
in the config file.
o Don't even try to probe I/O ranges that have been seen already.
o If we conflict with an IRQ or DRQ, then fail the probe.
Requested by: bde, gibbs
Approved by: jkh
