patch to allow btree indices on BYTEA

In a current project, I would like to store small binary data in some
fields of a database. PostgreSQL does not support the BINARY or
VARBINARY types, and it appears that VARCHAR is not safe for \000s
(and lexically sorts anyhow), so I have been using BYTEA.
Unfortunately, PostgreSQL 7.0.3 lacks the operations necessary to
build indices on BYTEA types. The included patch implements the
missing operations.

I wasn't able to find any guidelines on choosing OIDs, other than
"don't choose ones already in use or obviously reserved", so I have
made use of the range 1900-1916.

If there isn't a better way to do what I'm trying to do, I'd
appreciate seeing this in a future PostgreSQL release.

--Jered Floyd
jered(at)permabit(dot)com