pgsql: Fix collations when we call transformWhereClause from outside th

Fix collations when we call transformWhereClause from outside the parser.

Previous patches took care of assorted places that call transformExpr from
outside the main parser, but I overlooked the fact that some places use
transformWhereClause as a shortcut for transformExpr + coerce_to_boolean.
In particular this broke collation-sensitive index WHERE clauses, as per
report from Thom Brown.  Trigger WHEN and rule WHERE clauses too.

I'm not forcing initdb for this fix, but any affected indexes, triggers,
or rules will need to be dropped and recreated.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/d8d429890d6aa0246e28faa187a55cb0c65efd6e

Modified Files
--------------
src/backend/commands/trigger.c     |    3 +++
src/backend/parser/parse_utilcmd.c |    6 ++++++
2 files changed, 9 insertions(+), 0 deletions(-)