The semantics of this call allowed it to be called more than once when
parsing a message to restart a parse. This is not likely to be
useful in practice, and it also makes reading file descriptors
more complicated. Consequently this function has been removed and
replaced with with libipm_msg_in_get_msgno()
Normally the test runners run in 'forking mode'. When a lot of
messages are logged to stdout, the child process can still be writing
data when the parent writes 'ok' or 'not ok'. This can confuse
the tap-driver.sh process.
