Temporarily merges google internal changes. The javascript tests are
still failing and require additional investigation.

For fixing MSVC

Linking the cpp implementation extension statically with libprotobuf

Remove duplicate test cases.

Add -position and -isAtEnd for use when manually parsing input streams.

(NCrunch noticed these.)

Introduce a new nuget package, Google.Protobuf.Tools, basically to contain protoc on multiple platforms.

stubs/common.h undefines the GetMessage macro introduced in windows.h
map_test however include stubs/common.h before windows.h is transitively
included. This hack force map_test.cc to include windows.h first, so we
have a chance to undefine the GetMessage macro.

Added an API to allow oversize protos when using C++ extension in Python

Replace #include <iostream> with #include <ostream> in int128.cc

Referencing data member table_ in static functions break certain
platforms. Change it to refer to the declare type void** instead.

Introduce a new nuget package, Google.Protobuf.Tools, basically to contain protoc on multiple platforms.

I've moved both protoc.exe and the proto files out of Google.Protobuf.
The .proto files aren't a slam-dunk, but it feels like they belong with protoc as you'd *use* them with protoc.
It's not clear to me whether we really need both an x86 and x64 version of protoc.exe, as x86 would work on 64-bit Windows anyway. Discuss :)

Refactoring of FieldDescriptor

iostream is not actually necessary here, and it introduces unnecessary
static initializers.

Use the T() instead of NULL for the default value.

Add support for running on Jenkins

This makes no externally visible behavioral changes. Internally and non-behaviorally:

- We use a field (compiler-generated) to store the JsonName to avoid recomputing it repeatedly
- The documentation for JsonName is updated to reflect the meaning better
- Readonly autoprops and expression-bodied properties used where possible

csharp: add support for the json_name option

The template can be specialized on primitives, e.g. double, where
converting NULL will trigger a warning.

Mark iOS tests as able to fail.