update Gemfile - handle gems based on whether we're JRuby 1.7 / Java 7
we're going to release 0.7 that uses tomcat-jdbc instead of tomcat-dbcp !
update dependent gems to depend on 0.7 of the main dbpool gem
update tomcat-dbcp (we'll be keeping it for a while for compatibility)
switch to Tomcat's JDBC pool (by default)
more flexible setup + still support DBCP pool using the `pool: dbcp` option