Only the aggregate variant for now.

It raises an error for all types not having a btree or hash opclass.

It won't ever be called in a valid context with the current grammar
and is on top of the error list.

Closes #6.

Fixes #5.  Error rate is reduced by 20%.

fixes #4, fixes #7

Fix syntax errors in log.sql.

Drive-by-change: Add more indentation.

Otherwise the function that was picked cannot always be identified
unambiguously.

README: Add OSX build instructions