Twiddle around with Ruby versions

* Remove .rvmrc in favour of (private) .ruby-{version,gemset}.
* Change Travis config to run in "jruby" and only jdk7, because installing exact versions of jruby no longer works, and jdk6 isn't supported either.
Attempt to use bundler.rubygems.org directly

This should avoid endless redirect loop in bundler
Add Gemfile.lock, which changed after last commit
Compile with deprecation warnings, and remove a source of such warnings
Add .dump and .load for ActiveRecord compatibility

This closes #12