Modernize the Rakefile and gemspec.
Use sqlite3 instead of amalgalite.

Amalgalite won't compile against Ruby 1.9.3, and the maintainer doesn't
seem interested in releasing a new gem.
Fix an off by one error in mailbox scanning. [Fixes #48]

This resulted in mailboxes containing only one message sometimes not
being copied from the source, or winding up with duplicates on the
destination.
Release 1.1.2.