In the case of using q3map2 with 'build monitoring', the output of
q3map2 was being written twice, once for the logs received through the
'watchbsp' net connection and once as the fork/subprocess that actually
runs q3map2 was using the same stdout file descriptor as
netradiant-custom itself.
In order to prevent this, we redirect stdout/stderr to /dev/null in case
we use q3map2 with build monitoring for the subprocess and rely on the
received logs, which also get written to netradiant-custom's QT console.