pgsql: Make walreceiver send a reply after receiving data but before fl

Make walreceiver send a reply after receiving data but before flushing it.

It originally worked this way, but was changed by commit
a8a8a3e0965201df88bdfdff08f50e5c06c552b7, since which time it's been impossible
for walreceiver to ever send a reply with write_location and flush_location
set to different values.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/30f6136f28a6bf9eedcbf41038d5b021169bc0b9

Modified Files
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src/backend/replication/walreceiver.c |    3 +++
1 files changed, 3 insertions(+), 0 deletions(-)