pgsql: Fix some issues in pg_class.relminmxid and pg_database.datminmxi

Fix some issues in pg_class.relminmxid and pg_database.datminmxid documentation.

- Correct the name of directory which those catalog columns allow to be shrunk.
- Correct the name of symbol which is used as the value of pg_class.relminmxid
  when the relation is not a table.
- Fix "ID ID" typo.

Backpatch to 9.3 where those cataog columns were introduced.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/38d500ac2e5d4d4f3468b505962fb85850c1ff4b

Modified Files
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doc/src/sgml/catalogs.sgml |   12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)