+ # Expects $!,$? as set by close - see below.
+ # To use with system(), set $?=-1 first.
+ #
+ # Actual behaviour of perl operations:
+ # success $!==0 $?==0 close of piped open
+ # program failed $!==0 $? >0 close of piped open
+ # syscall failure $! >0 $?=-1 close of piped open
+ # failure $! >0 unchanged close of something else
+ # success trashed $?==0 system
+ # program failed trashed $? >0 system
+ # syscall failure $! >0 unchanged system