(1) nccl submodule, cnmem submodule
(2) mpi ops fallback test
(3) a bit more blob interface
(4) fixed tests
(5) caffe2.python.io -> caffe2.python.dataio to avoid name conflicts
(6) In the build system autogen __init__.py instead of having manual
rules just to copy over an empty __init__.py.
(1) Loss: do not coerce a gradient output. Although it may be numerically more efficient to do so, it makes the definition of a loss kind of funny if one does not really want to run backward pass.
(2) Autodifferentiation: allow more explicit in-place check, in-place is now opt-in, and implemented a simple SSA/IR gradient generation scheme. Also added some core gradient tests.
Misc bugfixes as well.
(1) various bugfixes.
(2) Tensor is now a class independent from its data type. This allows us
to write easier type-independent operators.
(3) code convention changes a bit: dtype -> T, Tensor<*Context> -> Tensor* alias.
(4) ParallelNet -> DAGNet to be more consistent with what it does.
(5) Caffe's own flags library instead of gflags.
(6) Caffe's own logging library instead of glog, but glog can be chosen with
compile-time definition -DCAFFE2_USE_GOOGLE_GLOG. As a result, glog macros
like CHECK, DCHECK now have prefix CAFFE_, and LOG(*) now becomes
CAFFE_LOG_*.
(7) an optional protobuf inclusion, which can be chosen with USE_SYSTEM_PROTOBUF
in build_env.py.
