Fix invalid offsetof warning.

Fix typo.

Use composition instead of inheritance for oneof default.

Verified test succeed under draconian heap checker

Bump csharp version

Update change log

Merge master into 3.4.x

Previous code duplicates io_win32.cc in sources of all the libraries
that include io_win32.h header.

CMake: Install .pc Files (Backport: 3.4)

Add declaration for AddDescriptorsImpl()

Update version number for 3.4.0

Omit the zip test if tools are not available

Use keys() instead of iterkeys() to be python3 compatbile.

Create 3.4.x branch

AddDescriptorsImpl() is a private static implementation detail,
and needs to be declared but won't be used from outside the
source file.  Place it inside an anonymous namespace to fix a
previous build error that would result in more restrictive
build enviornments that use -Werror=missing-declarations or
similar compiler flags.

Proto2 test message support to conformance test

Windows: support long paths in open/mkdir/access