Added a connection pool using tomcat-jdbc-pool to SQLite and MySQL
Since we handle the database connections in a different thread this is
necessary to ensure thread safety and will also improve performance on
large servers with heavy warp usage since we connect upon every usage to
update the visit counter).

The library that provides the connection pool is provided with the
plugin's jar, so we can change it if we ever need to. As of writing,
(probably faster) BoneCP is not an option as it requires gueva...
Pushed bukkit to 1.5.1-R0.1-SNAPSHOT in pom.xml
Added 1.5 blocks to warp-safety and cleaned up the corresponding method