pgsql: Renumber CHECKPOINT_* flags.

Renumber CHECKPOINT_* flags.

Commit 7dbb6069382 added a new CHECKPOINT_FLUSH_ALL flag. As that
commit needed to be backpatched I didn't change the numeric values of
the existing flags as that could lead to nastly problems if any
external code issued checkpoints. That's not a concern on master, so
renumber them there.

Also add a comment about CHECKPOINT_FLUSH_ALL above
CreateCheckPoint().

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/11abd6c90f1094eaeee32e1c57d250c9db5102cb

Modified Files
--------------
src/backend/access/transam/xlog.c |    1 +
src/include/access/xlog.h         |   10 +++++-----
2 files changed, 6 insertions(+), 5 deletions(-)