pgsql: Further code review for pg_lsn data type.

Further code review for pg_lsn data type.

Change input function error messages to be more consistent with what is
done elsewhere.  Remove a bunch of redundant type casts, so that the
compiler will warn us if we screw up.  Don't pass LSNs by value on
platforms where a Datum is only 32 bytes, per buildfarm.  Move macros
for packing and unpacking LSNs to pg_lsn.h so that we can include
access/xlogdefs.h, to avoid an unsatisfied dependency on XLogRecPtr.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/694e3d139a9d090c58494428bebfadad216419da

Modified Files
--------------
src/backend/utils/adt/pg_lsn.c       |   38 +++++++++++++++++-----------------
src/include/catalog/pg_type.h        |    2 +-
src/include/fmgr.h                   |    2 --
src/include/postgres.h               |   14 -------------
src/include/utils/pg_lsn.h           |    7 +++++++
src/test/regress/expected/pg_lsn.out |   10 ++++-----
6 files changed, 32 insertions(+), 41 deletions(-)