pgsql: Use WaitLatch, not pg_usleep, for delaying in pg_sleep().

Use WaitLatch, not pg_usleep, for delaying in pg_sleep().

This avoids platform-dependent behavior wherein pg_sleep() might fail to be
interrupted by statement timeout, query cancel, SIGTERM, etc. Also, since
there's no reason to wake up once a second any more, we can reduce the
power consumption of a sleeping backend a tad.

Back-patch to 9.3, since use of SA_RESTART for SIGALRM makes this a bigger
issue than it used to be.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/a64ca63e59c11d8fe6db24eee3d82b61db7c2c83

Modified Files
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src/backend/utils/adt/misc.c | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)