pgsql: Add sequence USAGE privileges to information schema

Add sequence USAGE privileges to information schema

The sequence USAGE privilege is sufficiently similar to the SQL
standard that it seems reasonable to show in the information schema.
Also add some compatibility notes about it on the GRANT reference
page.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/82e83f46a2ed311c6e7536f607f73a6f2a1d7dea

Modified Files
--------------
doc/src/sgml/information_schema.sgml       |   13 +++++++--
doc/src/sgml/ref/grant.sgml                |   12 +++++++++
src/backend/catalog/information_schema.sql |   37 ++++++++++++++++++++++++++++
3 files changed, 59 insertions(+), 3 deletions(-)