add Rails 4.2.0.beta1 to build for master
cherry-picked from 3.0-stable
Revert "add Rails 4.2.0.beta1 to build for master"

This reverts commit c17d2476025a23d0b81a959ee4e90f0c16f405d6.
CHANGELOG catch-up
change VERSION in master to 3.1.0.pre
update README to reflect the 3.0.0 release