For queries built from a table and filters, use a specialised count query
that only takes into account the where part of the statement. This will
speed-up the Browse Data tab for big tables.
See issue #1666
Make strings translatable, remove some more debug code, fix tests,
reduce size of patch slightly, remove weird tooltip, don't crash when
closing database, simplify code, fix filters, don't link agains pthread
on Windows.
