io_win32: support non-ASCII paths

Unlike GetEnvironmentVariableW,
GetCurrentDirectoryW doesn't set
ERROR_INSUFFICIENT_BUFFER.

If the test cannot find a temp directory by
checking environment variables, it will fall back
to using the current working directory as the temp
directory root.

This is what the test used to do as of commit
https://github.com/google/protobuf/commit/6de51caed52d798815954646b230c5aef3e4d2fc
and what was then changed by commit
https://github.com/google/protobuf/pull/3978/commits/792d098769d8e000d8d474c8ffd201d2eabc2134

Fixes https://github.com/google/protobuf/issues/3951

Do not use "googletest.h", apprently that leads to
linking errors on Windows which I couldn't figure
out how to solve, and decided to just go with
plain gTest instead.

See https://github.com/google/protobuf/issues/3951

* Provide discardUnknownFields API in php implementation

* Provide discardUnknownFields API in php c extension.

Add _file_desc_by_toplevel_extension back

Add _file_desc_by_toplevel_extension back for compatibility issue with 3.4.1.

_file_desc_by_toplevel_extension is a temporary solution for FieldDescriptor.file.
FieldDescriptor.file was added in code gen. However, we need to keep it for some time for compatibility reason (with 3.4.1 only). May try to remove it after 2 years.

Add protobuf-all in post release

conflict

Support win32 long path for cross compiled build

Update changelog

Backport #3858 to 3.5.x branch

Fix Atomic32/AtomicWord on some platforms.

- Removed the redefination in the atomicword_compat.h. Now Atomic32 will
alwyas be intptr_t in 32bit platforms, the bridge is no longer needed.
- Change NaCl 64bit to use intptr_t instead of int32 for Atomic32,
otherwise AtmoicWord APIs will miss the definations.

After this change, the AtmoicWord will always be either Atomic32 or
Atmoic64 depending on the platforms.

Update version number to 3.5.0

* Fix php well known type conformance tests

* Properly generate code for test.proto

* Provide GPBMetadata files in c extensions for generated files to import.

* Remove unnecessary test

* Clean up code

* Add declaration for initOnce.

* Refactoring