pgsql: Move LockClauseStrength, LockWaitPolicy into new file nodes/lock

Move LockClauseStrength, LockWaitPolicy into new file nodes/lockoptions.h.

Commit df630b0dd5ea2de52972d456f5978a012436115e moved enum LockWaitPolicy
into its very own header file utils/lockwaitpolicy.h, which does not seem
like a great idea from here. First, it's still a node-related declaration,
and second, a file named like that can never sensibly be used for anything
else. I do not think we want to encourage a one-typedef-per-header-file
approach. The upcoming foreign table inheritance patch was doubling down
on this bad idea by moving enum LockClauseStrength into its *own*
can-never-be-used-for-anything-else file. Instead, let's put them both in
a file named nodes/lockoptions.h. (They do seem to need a separate header
file because we need them in both parsenodes.h and plannodes.h, and we
don't want either of those including the other. Past practice might
suggest adding them to nodes/nodes.h, but they don't seem sufficiently
globally useful to justify that.)

Committed separately since there's no functional change here, just some
header-file refactoring.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/9fac5fd741ec17ae24dde6b8e82064f13c148ddf

Modified Files
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src/include/access/heapam.h | 2 +-
src/include/executor/executor.h | 1 -
src/include/nodes/lockoptions.h | 45 ++++++++++++++++++++++++++++++++++++
src/include/nodes/parsenodes.h | 11 +--------
src/include/nodes/plannodes.h | 2 +-
src/include/utils/lockwaitpolicy.h | 31 -------------------------
6 files changed, 48 insertions(+), 44 deletions(-)