Branch 130152575 (#3785)

* Place MutableHashTableOfTensors and MutableHashTable on the ps
Change: 130110569

* C++ API: Added a Const constructor for non-empty const supporting type cast.

Fixes #3752
Change: 130113000

* Add support for SDCAOptimizer within estimators.LinearRegressor.
Change: 130119827

* Relax strictness of num_outputs check.
Change: 130123064

* Update generated Python Op docs.
Change: 130127897

* Reduce number of allocations in EncodeTensorToByteBuffer by
hand-encoding the skeleton portion of the TensorProto (in particular,
encoding the TensorShapeProto was allocating one object per dimension
plus an allocation per Tensor).

Reduces total number of allocations for an RPC-intensive benchmark
from 77.4M to 70.9M (-8.4%).
Change: 130132140

* Add support for weighted inputs to CountExtremelyRandomStats.
Change: 130132347

* Fix opensource_build.
Change: 130138675

* Makes it more convenient to construct Counters.

- By forwarding the metric-def arguments, so that the caller doesn't have to
  provide braces.
Change: 130142393

* Add a new parse_tensor op for parsing a serialized TensorProto into a Tensor.
Change: 130143090

* Update FeedingQueueRunner to match the _run function in the original QueueRunner.
Change: 130145852

* Update ops-related pbtxt files.
Change: 130146203

* Update generated Python Op docs.
Change: 130146772

* Merge changes from github.
Change: 130150683

* Update generated Python Op docs.
Change: 130151290

* third_party/tensorflow/core: Use macro __linux__ instead of __linux

Some Linux gcc installations, with some flags, do not set __linux,
but all tested so far seem to set __linux__.

An example if gcc on linux on ppc64.  If the compiler is invoked with a flag
the defines a particular standard (such as -std=c++11 or -std=c++0x or -std=c89
or -std=c99) then "linux" and "__linux" are not defined.  The macro "__linux__"
is always set regardless of these options.

This led to Linux-specific implementations of certain things being avoided on
ppc64.

The web page
        https://sourceforge.net/p/predef/wiki/OperatingSystems/
says that the macros
        linux __linux
are obsoltete and __linux__ is preferred, though it's unclear how definititve
that page is.
Change: 130152575