Group variables a bit.
Do decrease low when a bogus low pulse was received, this should make
detecting receiver errors more reliable.
Clean up code a bit, no functional changes (GETBIT_RECV and GETBIT_XMIT
are intended to be mutually exclusive).
Display counters on transmitter errors.
count is not assigned here, so no need to protect for a divide-by-zero here.
Re-indent, and lose a goto statement by joining if statements.
Keep track of the estimated actual minute length (wall clock time). The
idea is that this should prevent that the clock wanders off if no useable
data is being received.
Only increase the accumulated minute length on end-of-minute when
receiving a live signal, it is already increased for the from-file signal.
If there is a timeout (> 2.5 times a normal second length), then this
case is also valid for a transmitter error (all high pulses), so handle
that case together with a receiver error (all low pulses).

Add another case for a read error (timeout but high and low pulses).
The passed wall-clock time is also 2.5 seconds for a transmitter error.
Display the accumulated minute length upon end-of-minute.
Only decode the date/time and civil warning information (and reset the
accumulated minute length) if this is the first minute or if the minute
is long enough.

This should prevent the time wandering off in case of a bad radio signal,
caused by the add_minute() calls.
Also display the accumulated minute length in case of short non-initial
minute.