Rename 'cmd' to 'cmd_name' in CreatePolicyStmt

Stephen Frost <sfrost@snowman.net>

Commit: 3c99788797e8269ac19c7c8e3fb99dd9613646ea
Author: Stephen Frost <sfrost@snowman.net>
Date: 2015-08-21T12:22:22Z
Releases: 9.6.0
Rename 'cmd' to 'cmd_name' in CreatePolicyStmt

To avoid confusion, rename CreatePolicyStmt's 'cmd' to 'cmd_name',
parse_policy_command's 'cmd' to 'polcmd', and AlterPolicy's 'cmd_datum'
to 'polcmd_datum', per discussion with Noah and as a follow-up to his
correction of copynodes/equalnodes handling of the CreatePolicyStmt
'cmd' field.

Back-patch to 9.5 where the CreatePolicyStmt was introduced, as we
are still only in alpha.

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