pgsql: Fix subtly-wrong volatility checking in BeginCopyFrom().

Fix subtly-wrong volatility checking in BeginCopyFrom().

contain_volatile_functions() is best applied to the output of
expression_planner(), not its input, so that insertion of function
default arguments and constant-folding have been done. (See comments
at CheckMutability, for instance.) It's perhaps unlikely that anyone
will notice a difference in practice, but still we should do it properly.

In passing, change variable type from Node* to Expr* to reduce the net
number of casts needed.

Noted while perusing uses of contain_volatile_functions().

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/060b22a99a67e01aa097f1a21d2123f166ccdb15

Modified Files
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src/backend/commands/copy.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)