Testsuite: 0322 (pipelining errors) avoid triggering SIGPIPE

Testsuite: 0322 (pipelining errors) avoid triggering SIGPIPE

This was timing-dependent; if the exim closed the connection before
the script wrote to it _after_ triggerring an error, EPIPE/SIGPIPE.
Unexplained as yet: why runtest (perl) saw this as a 141 server
returncode (NB: 141-128 = 13 = SIGPIPE, the shell behaviour) when
"perldoc -v '$?'" (which runtest is coded to) says that a signum
should be in the top nibble of 16b.