pgsql: Add an errdetail_internal() ereport auxiliary routine.

Add an errdetail_internal() ereport auxiliary routine.

This function supports untranslated detail messages, in the same way that
errmsg_internal supports untranslated primary messages. We've needed this
for some time IMO, but discussion of some cases in the SSI code provided
the impetus to actually add it.

Kevin Grittner, with minor adjustments by me

Branch
------
REL9_1_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/657836741410563be35180ba34adcdae6c767ce5

Modified Files
--------------
doc/src/sgml/sources.sgml | 25 ++++++++++++++++++-------
src/backend/utils/error/elog.c | 27 +++++++++++++++++++++++++++
src/include/utils/elog.h | 6 ++++++
3 files changed, 51 insertions(+), 7 deletions(-)