pgsql: Add some additional core functions to support join pushdown for

Add some additional core functions to support join pushdown for FDWs.

GetExistingLocalJoinPath() is useful for handling EvalPlanQual rechecks
properly, and GetUserMappingById() is needed to make sure you're using
the right credentials.

Shigeru Hanada, Etsuro Fujita, Ashutosh Bapat, Robert Haas

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/a104a017fc5f67ff5d9c374cd831ac3948a874c2

Modified Files
--------------
doc/src/sgml/fdwhandler.sgml  |  32 +++++++++
src/backend/foreign/foreign.c | 164 +++++++++++++++++++++++++++++++++++++++++-
src/include/foreign/fdwapi.h  |   1 +
src/include/foreign/foreign.h |   1 +
4 files changed, 196 insertions(+), 2 deletions(-)