pgsql: Revert "Replace PostmasterRandom() with a stronger way of genera

Revert "Replace PostmasterRandom() with a stronger way of generating randomness."

This reverts commit 9e083fd4683294f41544e6d0d72f6e258ff3a77c. That was a
few bricks shy of a load:

* Query cancel stopped working
* Buildfarm member pademelon stopped working, because the box doesn't have
  /dev/urandom nor /dev/random.

This clearly needs some more discussion, and a quite different patch, so
revert for now.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/faae1c918e8aaae034eaf3ea103fcb6ba9adc5ab

Modified Files
--------------
contrib/pgcrypto/Makefile           |   2 +-
contrib/pgcrypto/internal.c         |  40 +++---
contrib/pgcrypto/random.c           | 247 ++++++++++++++++++++++++++++++++++++
src/backend/libpq/auth.c            |  27 +---
src/backend/postmaster/postmaster.c | 153 ++++++++++++++++------
src/include/port.h                  |   3 -
src/port/Makefile                   |   2 +-
src/port/pg_strong_random.c         | 148 ---------------------
src/tools/msvc/Mkvcbuild.pm         |   6 +-
9 files changed, 384 insertions(+), 244 deletions(-)