pgsql: Add pg_describe_object function

Add pg_describe_object function

This function is useful to obtain textual descriptions of objects as
stored in pg_depend.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=6cc2deb86e9183262493a6537700ee305fb3e096

Modified Files
--------------
doc/src/sgml/func.sgml           |   12 ++++++++
src/backend/catalog/dependency.c |   57 ++++++++++++++++++++------------------
src/include/catalog/catversion.h |    2 +-
src/include/catalog/pg_proc.h    |    2 +
src/include/utils/builtins.h     |    3 ++
5 files changed, 48 insertions(+), 28 deletions(-)