Update the comment on the message_type to cover what it should be.

Objc proto2 conformance test support

- Better error message for unknown messageType.
- Remove unneeded if.

Both test_messages_proto3.proto & test_messages_proto2.proto define
message ForeignMessage {...} and enum ForeignEnum {...} but since
objc doesn't use the proto package in the naming, these end up
conflicting.

Adding the objc_class_prefix option to the proto3 file ensure the generated
objc types are all unique.

Fix issue #1745 - javascript allow dot in filename

Add declaration for AddDescriptorsImpl()

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

Treat missing declarations as an error for test builds, to prevent
future updates which add functions without properly declaring them.
This will prevent broken builds in more restrictive build environments.

CMake: Install .pc Files

Exclude the unconfigured .pc input files of the CMake
based install: they shall not be packed/distributed,
only their outputs are

Adds pkg-config (`.pc`) files for CMake based installs.

Updated outdated hyperlink

Github repo had moved, pointing to correct location.

Fix typos in comment

Fixed default instance initialization for C++ lite

Make it compatible with python 3.6.1

An ifdef condition seems to have been inverted by mistake, causing the
dynamic initialization to occur for lite if and only if the
_NO_STATIC_INITIALIZER macro is set. This problem manifested itself as
segfaults due to uninitialized empty strings:
https://github.com/google/protobuf/issues/2839

Since no one complained about initialization not happening, it would
appear that we can just disable this initialization for lite
unconditionally, so that is what this change does. Instead of the
default instance initialization happening pre-main, it now always
happens lazily when needed.

Merge 3.3.x into master

Add note about includes to README

Set PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION for pure python comformance

Ran into an issue today where a machine had the `protoc` compiler but not the include files. Took a while to sort out, and this added note to the README included in every zip should help.

* Add php_generic_services option

* Generate PHP generic services

* Respect namespaces for generated PHP services

* Test PHP generated services

* Rename PHP generator service method doc comment function

* Correct phpdoc service method case

* Test namespaced PHP generic services

* Always use the FQCN for PHP generic service input/output

* Add generated_service_test to php test.sh

* Add php service test protos to CI

* Add php service files to php_EXTRA_DIST

* Use Interface suffix for php generic services

Fix map_field_inl.h for gcc 4.1

Fix build when using -Werror=undef

Issue 3112: Object class with fully qualified name

Expand documentation in Readme.md

* remove pass by reference for php setters

* comments out memory leak test