Rename AtRefBackend's internal_put into get_and_set.
Rename AtRefBackend's internal_put into get_and_set.

rranelli/thread_safe,headius/thread_safe,ruby-concurrency/thread_safe,rranelli/thread_safe,ruby-concurrency/thread_safe,rranelli/thread_safe,headius/thread_safe,ruby-concurrency/thread_safe