update JDBC driver loading to handle latest jdbc gems
latest gems no longer auto-load the driver jar but instead provide a load_driver method, this change is handled backward compatible (since not all driver gems are updated + users might decide to stick with an older gem version).
Attempt to use the jdbc-hsqldb driver if available

Sequel only supports HSQLDB 2.2+.  Previously, the jdbc-hsqldb
gem was at version 1.8.1.3.  However, it has recently been upgraded
to 2.2.9, and Sequel now supports it, so load it automatically
so that the jar does not need to be loaded manually.
Allow treating tinyint(1) unsigned columns as booleans in the mysql adapters

Previously, the schema type for tinyint(1) unsigned columns would
be integer instead of boolean.
Add some warnings to the documentation related to Object#extend use

Object#extend busts method caches in MRI and probably other current
ruby implementations, so note usage in the documentation so that
users can be aware of it.
Support default_schema when reseting primary key sequences on PostgreSQL (Fixes #596)
Handle schema-qualified row_types in the pg_array integration in the pg_row extension (Fixes #595)

This isn't a bulletproof fix, but it does fix the issue in most
cases.  A more complete fix would handle quoting of the type
names.