pgsql: Adjust collation determination rules as per discussion.

Adjust collation determination rules as per discussion.

Remove crude hack that tried to propagate collation through a
function-returning-record, ie, from the function's arguments to individual
fields selected from its result record.  That is just plain inconsistent,
because the function result is composite and cannot have a collation;
and there's no hope of making this kind of action-at-a-distance work
consistently.  Adjust regression test cases that expected this to happen.

Meanwhile, the behavior of casting to a domain with a declared collation
stays the same as it was, since that seemed to be the consensus.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/a19002d4e5da028ff7280554b281e402c609898b

Modified Files
--------------
src/backend/parser/parse_collate.c               |   27 ++---------
src/backend/parser/parse_func.c                  |    2 +-
src/backend/parser/parse_target.c                |    2 +-
src/test/regress/expected/collate.linux.utf8.out |   54 +++++++++++-----------
src/test/regress/expected/collate.out            |   32 ++++++------
src/test/regress/sql/collate.linux.utf8.sql      |   10 ++--
src/test/regress/sql/collate.sql                 |    8 ++--
7 files changed, 59 insertions(+), 76 deletions(-)