Mostly these are just comments but there are a few in documentation
and a handful in code and tests. Hopefully this doesn't cause too much
unnecessary pain for backpatching. I relented from some of the most
common like "thru" for that reason. The rest don't seem numerous
enough to cause problems.

Thanks to Kevin Lyda's tool https://pypi.python.org/pypi/misspellings

Was part of box type in SP-GiST index patch.

Reported-by: Emre Hasegeli

My compiler doesn't like the lack of initialization of "flag", and
I think it's right: if there were zero keys we'd have an undefined
result.  The AND of zero items is TRUE, so initialize to TRUE.

Patch implements quad-tree over boxes, naive approach of 2D quad tree will not
work for any non-point objects because splitting space on node is not
efficient. The idea of pathc is treating 2D boxes as 4D points, so,
object will not overlap (in 4D space).

The performance tests reveal that this technique especially beneficial
with too much overlapping objects, so called "spaghetti data".

Author: Alexander Lebedev with editorization by Emre Hasegeli and me