pgsql: Record data_checksum_version in control file.

Record data_checksum_version in control file.
The value is not used anywhere in code, but will
allow future changes to the checksum version
should that become necessary in the future.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/443951748ce4c94b001877c7cf88b0ee969c79e7

Modified Files
--------------
src/backend/access/transam/xlog.c       |    6 +++---
src/backend/bootstrap/bootstrap.c       |    5 +++--
src/bin/pg_controldata/pg_controldata.c |    4 ++--
src/bin/pg_resetxlog/pg_resetxlog.c     |    4 ++--
src/include/catalog/pg_control.h        |    4 ++--
src/include/storage/bufpage.h           |    5 ++++-
6 files changed, 16 insertions(+), 12 deletions(-)