pgsql: Avoid an unnecessary syscache lookup in parse_coerce.c.

Avoid an unnecessary syscache lookup in parse_coerce.c.

All the other fields of the constant are being extracted from the syscache
entry we already have, so handle collation similarly.  (There don't seem
to be any other uses for the new function at the moment.)

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/c5ff3ff49229e8fb7da0e46b463bfc9b12219078

Modified Files
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src/backend/parser/parse_coerce.c |    2 +-
src/backend/parser/parse_type.c   |   16 +++++++++++++---
src/include/parser/parse_type.h   |    1 +
3 files changed, 15 insertions(+), 4 deletions(-)