Fix EXPLAIN tests for 9.4

9.4 adds a "Planning time" line to simple "EXPLAIN" output. Fix by using
"EXPLAIN (costs off)".
Merge pull request #77 from ChristophBerg/explain-9.4

Fix EXPLAIN tests for 9.4
Fix access to column metadata.

Should be compatbile from SQLAlchemy 0.7.8 to the latest 0.9.7
Fixes #79
Correct Makefile for vpath builds

Building out-of-tree/in a subdirectory needs some fixes to make sure the
proper references to the VPATH or srcdir directories are used.

Signed-off-by: Christoph Berg <myon@debian.org>