This lets BRIN be used with R-Tree-like indexing strategies.
Also provided are operator classes for range types, box and inet/cidr.
The infrastructure provided here should be sufficient to create operator
classes for similar datatypes; for instance, opclasses for PostGIS
geometries should be doable, though we didn't try to implement one.
(A box/point opclass was also submitted, but we ripped it out before
commit because the handling of floating point comparisons in existing
code is inconsistent and would generate corrupt indexes.)
Author: Emre Hasegeli. Cosmetic changes by me
Review: Andreas Karlsson
b0b7be6133