pgsql: Don't duplicate log_checkpoint messages for both of restart and

Don't duplicate log_checkpoint messages for both of restart and checkpoints.

The duplication originated in cdd46c765, where restartpoints were
introduced.

In LogCheckpointStart's case the duplication actually lead to the
compiler's format string checking not to be effective because the
format string wasn't constant.

Arguably these messages shouldn't be elog(), but ereport() style
messages. That'd even allow to translate the messages... But as
there's more mistakes of that kind in surrounding code, it seems
better to change that separately.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/5e5b65f359b7a12c05708585a8e6cd4d80ca2652

Modified Files
--------------
src/backend/access/transam/xlog.c | 62 +++++++++++--------------------------
1 file changed, 18 insertions(+), 44 deletions(-)