pgsql: Change the relkind for partitioned tables from 'P' to 'p'.

Change the relkind for partitioned tables from 'P' to 'p'.

Seven of the eight other relkind codes are lower-case, so it wasn't
consistent for this one to be upper-case. Fix it while we still can.

Historical notes: the reason for the lone exception, i.e. sequences being
'S', is that 's' was once used for "special" relations. Also, at one time
the partitioned-tables patch used both 'P' and 'p', but that got changed,
leaving only a surprising choice behind.

This also fixes a couple little bits of technical debt, such as
type_sanity.sql not knowing that 'm' is a legal value for relkind.

Discussion: https://postgr.es/m/27899.1488909319@sss.pgh.pa.us

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/8b358b42f8eb6156a82ac9a41fc4e8335c8dc37a

Modified Files
--------------
doc/src/sgml/catalogs.sgml | 13 +++++----
src/backend/catalog/information_schema.sql | 44 ++++++++++++++++--------------
src/backend/catalog/system_views.sql | 4 +--
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_class.h | 11 ++++----
src/test/regress/expected/create_table.out | 2 +-
src/test/regress/expected/rules.out | 4 +--
src/test/regress/expected/sanity_check.out | 2 +-
src/test/regress/expected/type_sanity.out | 2 +-
src/test/regress/sql/sanity_check.sql | 2 +-
src/test/regress/sql/type_sanity.sql | 2 +-
11 files changed, 47 insertions(+), 41 deletions(-)