pgsql: If the stats collector dies during Hot Standby, restart it.

If the stats collector dies during Hot Standby, restart it.

This bug exists as far back as 9.0, when Hot Standby was introduced,
so back-patch to all supported branches.

Report and patch by Takayuki Tsunakawa, reviewed by Michael Paquier
and Kuntal Ghosh.

Branch
------
REL9_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/4a8cfbdcbe8447e4226b2ebdb155e0acc1167db5

Modified Files
--------------
src/backend/postmaster/postmaster.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)