pgsql: Fix postmaster to attempt restart after a hot-standby crash.

Fix postmaster to attempt restart after a hot-standby crash.

The postmaster was coded to treat any unexpected exit of the startup
process (i.e., the WAL replay process) as a catastrophic crash, and not try
to restart it. This was OK so long as the startup process could not have
any sibling postmaster children. However, if a hot-standby backend
crashes, we SIGQUIT the startup process along with everything else, and the
resulting exit is hardly "unexpected". Treating it as such meant we failed
to restart a standby server after any child crash at all, not only a crash
of the WAL replay process as intended. Adjust that. Back-patch to 9.0
where hot standby was introduced.

Branch
------
REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/ef19c9dfaa99a2b78ed0f78aa4a44ed31636fdc4

Modified Files
--------------
src/backend/postmaster/postmaster.c | 13 +++++++++----
1 files changed, 9 insertions(+), 4 deletions(-)