pgsql: Bootstrap WAL to begin at segment logid=0 logseg=1 (000000010000

Bootstrap WAL to begin at segment logid=0 logseg=1 (000000010000000000000001)
rather than 0/0, so that we can safely use 0/0 as an invalid value. This is a
more future-proof fix for the corner-case bug in streaming replication that
was fixed yesterday. We had a similar corner-case bug with log/seg 0/0 back in
February as well. Avoiding 0/0 as a valid value should prevent bugs like that
in the future. Per Tom Lane's idea.

Back-patch to 9.0. Since this only affects bootstrapping, it makes no
difference to existing installations. We don't need to worry about the
bug in existing installations, because if you've managed to get past the
initial base backup already, you won't hit the bug in the future either.

Branch
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REL9_0_STABLE

Details
-------
http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=77459eba8cb32aa0e1e1736a3f3b08b8e8dde181

Modified Files
--------------
src/backend/access/transam/xlog.c | 21 ++++++++++++---------
src/backend/replication/walsender.c | 2 +-
2 files changed, 13 insertions(+), 10 deletions(-)