Move way full and relation full calls out of experimental

To clean-up old files, remove test/*experimental.log
Remove --enable-experimental from ./configure
Use the number of selected ways/relations in full calls

This is a slight optimization for queries against deleted nodes
as it avoids a select, but it is a significant improvement for
backends like pgsnapshot with no history because now no queries are
needed to check for non-existant ways
Create a new pgsnapshot backend

This backend is intended for a pgsnapshot database loaded with osmosis.

It supports all non-history calls and passes all openstreetmap-api-testsuite
tests for non-history calls. The most notable history call is the 404 vs 410
error code of single-element fetch calls.

There are not yet unit tests for the backend.