The mount() and bind() syscalls return -1 on error,
and the mountid sequence number on success.
The manpage states that the mountid sequence number
is a positive integer, but the kernels implementation
currently uses a unsigned 32-bit integer and does not
guarantee that the mountid will not become negative.
Most code just cares about the error, so test for
the -1 error value only.
Fix inconsistencies between programs and their usage
messages, correct instances where information seems
to be missing or lost. This includes missing arguments,
making usage consistent with manuals, and so on.
