pgsql: Assert that WaitLatch's timeout is not more than INT_MAX millise

Assert that WaitLatch's timeout is not more than INT_MAX milliseconds.

The behavior with larger values is unspecified by the Single Unix Spec.
It appears that BSD-derived kernels report EINVAL, although Linux does not.
If waiting for longer intervals is desired, the calling code has to do
something to limit the delay; we can't portably fix it here since "long"
may not be any wider than "int" in the first place.

Part of response to bug #7670, though this change doesn't fix that
(in fact, it converts the problem from an ERROR into an Assert failure).
No back-patch since it's just an assertion addition.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/14ddff44c22cb358775d5aad6953f0ce0fdb64cf

Modified Files
--------------
src/backend/port/unix_latch.c  |   10 ++++++----
src/backend/port/win32_latch.c |    3 ++-
2 files changed, 8 insertions(+), 5 deletions(-)