Updates for beta/rc stamping

FYI, Magnus just pointed out that src/include/pg_config.h.win32 had the
version string of 8.0devel rather than the correct 8.0.0rc1.

I have added a mention in tools/RELEASE_CHANGES that this file should be
updated during beta and rc as well as final release. This file is used
by VC and BCC for non-configure-run win32-client-only builds.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
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