Also move inline code for prod to proper .cc file.

This module provides feedback to the grammar on the failure rate of
productions to allow blacklisting them.

The idea was to test with a more conservative setting, but this causes
compatibility problems (OSX).

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