pgsql: Add missing check for wal_debug GUC.

Add missing check for wal_debug GUC.

9a20a9b2 added a new elog(), enabled when WAL_DEBUG is defined. The
other WAL_DEBUG dependant messages check for the wal_debug GUC, but this
one did not. While at it replace 'upto' with 'up to'.

Discussion: 20150610110253.GF3832@alap3.anarazel.de

Backpatch to 9.4, the first release containing 9a20a9b2.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/90231cd5188c43da94f58f7a839eee9286d0f864

Modified Files
--------------
src/backend/access/transam/xlog.c |    4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)