plug caffe2 into jit" (#16388)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16388
previous diff broke master -- this refactors out the custom_operator.cpp file into a separate header + cpp pair (caffe2_operator.{h,cpp})
Reviewed By: smessmer
Differential Revision: D13823550
fbshipit-source-id: 00e005e650336132d05aef97c1f0e5242ccad5ba
