[postgis-devel] default btree operators class

[strk]

I forgot to add functions definitions. Now committed.
Please update your CVS copy if you are trying postgis against PG7.4

Quick review:

We now have a default btree operator class which is used by PG7.4
to implement UNION, GROUP BY, DISTINCT and ORDER BY.

Prior to PG7.4 operators '>','<','=' where used for this purpose.
Starting from 7.4 it is *required* to define a default btree opclass
for that to work (or you get a "could not identify an ordering operator
for type geometry" error).

To support the btree operator class, comparision functions have been
added and existent ones (only used by the above SQL constructs) modified
to have a consistent implementation. Briefly they compare bounding boxes
sorting them numerically on LLB.x, LLB.y, LLB.z, URT.x, URT.y, URT.z keys
in that order. Equality is obtained when bounding boxes are approximately
the same (with a floating-point small error tolerance).

--strk;