Adjust collation determination rules as per discussion.

Tom Lane <tgl@sss.pgh.pa.us>

Commit: a19002d4e5da028ff7280554b281e402c609898b
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: 2011-04-09T18:40:09Z
Releases: 9.1.0
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.

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