pgsql: Add assign_expr_collations() to CreatePolicy() and AlterPolicy()

Add assign_expr_collations() to CreatePolicy() and AlterPolicy().

As noted by Noah Misch, CreatePolicy() and AlterPolicy() omit to call
assign_expr_collations() on the node trees. Fix the omission and add
his test case to the rowsecurity regression test.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/808ea8fc7bb259ddd810353719cac66e85a608c8

Modified Files
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src/backend/commands/policy.c             |   10 ++++++++++
src/test/regress/expected/rowsecurity.out |   21 +++++++++++++++++++++
src/test/regress/sql/rowsecurity.sql      |   12 ++++++++++++
3 files changed, 43 insertions(+)