Set non-blocking mode on the pty master file descriptor while

Set non-blocking mode on the pty master file descriptor while
the slave file descriptor is still held open since otherwise
the fcntl call can fail on FreeBSD (the child process might
have already exited and closed the slave file descriptor so we
have to keep it open in order to avoid FreeBSD potentially
generating an EAGAIN exception). This appoach is cleaner than
triggering the exception and being forced to handle it
somehow.

svn path=/main/trunk/; revision=7835