Re: executor relation handling

I've just completed a review of the v5 patch set. I ended up just
making the changes myself since Amit mentioned he was on leave for a
few weeks.

Summary of changes:

1. Changed the way we verify the lock already exists with debug
builds. I reverted some incorrect code added to LockRelationOid that
seems to have gotten broken after being rebased on f868a8143a9.  I've
just added some functions that verify the lock is in the
LockMethodLocalHash hashtable.
2. Fixed some incorrect lock types being passed into
addRangeTableEntryForRelation()
3. Added code in addRangeTableEntryForRelation to verify we actually
hold the lock that the parameter claims we do. (This found all the
errors I fixed in #2)
4. Updated various comments outdated by the patches
5. Updated executor README's mention that we close relations when
calling the end node function.  This is now handled at the end of
execution.
6. Renamed nominalRelation to targetRelation.  I think this fits
better since we're overloading the variable.
7. Use LOCKMODE instead of int in some places.
8. Changed warning about relation not locked to WARNING instead of NOTICE.
9. Renamed get_unpruned_rowmarks() to get_nondummy_rowmarks(). Pruning
makes me think of partition pruning but the function checks for dummy
rels. These could be dummy for reasons other than partition pruning.

I've attached a diff showing the changes I made along with the full
patches which I tagged as v6.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
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