Update the built-in SQLite to the latest 3.8.3 beta.  Fix a compiler
warning in the md5.c module.
Enhance support for recent versions of PostgreSQL.
Use standard engine naming for PostgreSQL as the tests already rely on it.
Skip MSSQL for several tests that are incompatible with it.
Update the built-in SQLite to 3.8.4 beta.
Update to the latest 3.8.4 beta from upstream.