Throw explanatory message rather than abort.
remove passing around of copy values sql string buffer and use only locally
Added point processor for multi-table output.

The point processor just looks at nodes to determine the output -
we should have another one which is able to do centroids for
matching types.

Added a test case for this and factored out a bunch of common code
for setting up test databases.
Merge remote-tracking branch 'MapQuest/kk_multiback' into mla_multi_backend