Fix pq_putmessage_noblock() to not block.
An evident copy-and-pasteo in commit
2bd9e412f broke the non-blocking
aspect of pq_putmessage_noblock(), causing it to behave identically to
pq_putmessage(). That function is nowadays used only in walsender.c,
so that the net effect was to cause walsenders to hang up waiting for
the receiver in situations where they should not.
Kyotaro Horiguchi
Patch: <
20160728.185228.
58375982.horiguchi.kyotaro@lab.ntt.co.jp>