Install prefix--unpackaged--1.2.0.sql, don't install prefix--1.1.sql
Convert most of the existing test files to regression tests

prefix.sql is TESTS.md without the gavel/explain part, falcon.sql and
queries.sql are just moved to the sql/ directory. The logic for doing
"create extension" vs "\i prefix--1.2.0.sql" was adapted from pgmp.
Ignore some temporary files in debian/
Bump version to 1.2.1
Add watch file.