* Fix ruby segment fault

1) rb_ary_new cannot be called during allocate function. During allocate
fucntion, the containing object hasn't been marked and rb_ary_new may
invoke gc to collect containing object.
2) The global map should be marked before allocating it. Otherwise it
may be garbage collected.

* Add test

* Remove commented code

* Fix grammer error

Objc increase test coverage

Add Xcode 9 support to the helper script.

ObjC: Fix merging of length delimited unknown fields.

- Add a test to cover this and tweak the test to not use two merge
  paths to be sure things are as expected.

* Use constexpr more with VC++ 2017

Chrome's official builds have over 170 dynamic initializers for
variables of the form *::TableStruct::aux. Defining
PROTOBUF_CONSTEXPR_VAR to be constexpr for VS 2017 gets rid of all of
these and saves about 10 KB of binary size.

* Update generated_message_table_driven.h

Restore accidentally deleted line.

generate python code when calling PROTOBUF_GENERATE_PYTHON

* Enforce all error report for php tests.

* Import vendor/autoload.php in tests/bootstrap_phpunit.php

protobuf_generate: add EXPORT_MACRO option

Test Shutdown can be called multiple times.

Allow initializing a chain of protos using only a hash in Ruby

* Add $ before url_prefix_len to make it a variable.

* Remove unnecessary string length check

* Remove useless $type_url_len

Fixed to_h with repeated messages to return hashes in Ruby

Conformance Tests for Null Timestamp and Duration JSON Values

Integrated internal changes from Google

Fix go example test.

It needs "-I" flag to find imported file google/protobuf/timestamp.proto

Clang warning cleanup for unused parameter.

Fix policy warning CMP0054

Google.Protobuf should target net45 (upport to upstream/master)

fix protobuf_generate function

Add bazel support for examples.

This addressbook.proto now belongs to its own bazel pacakge and can't be
accessed in bazel protobuf_test target.