update rails
remove unused checked class variable
fix join in ar 3x, fix issue #147
fix join in ar 4
fix join for ar 3.0 and 4.1
fix integration/active_record4/association_spec
remove checked from specs
use Thread.current instead of class variables
use add_runtime_dependency instead of add_dependency
add "Work with Sinatra" in README
add debug mode to output detail info
support mongoid 4, hack get_relation instead of set_relation
add mongoid 4 to test.sh
cleanup Gemfiles
do not test activerecord for mongoid tests
uncomment code in test code