Update php/release.sh to be executable and create a new branch

Down integrate to GitHub

* Compiler changes (extensions)

* Generated changes (extensions)

* Library changes (extensions)

* Adjusted a summary to indicate ContainingType can be null for extensions

* Compiler changes (custom option review + access level review)

* Generated code changes (custom options + access review)

* Library changes (custom options + access review)

* Support C# 6 with library changes

* Access HasValue by property

* Set access level of all extension classes to internal (revert in next PR)

* Added null checks to custom options

* Rebase on master and regenerate Conformance

* Removed second dictionary from ExtensionSet

* Rebased compiler changes

* Rebased generated code changes

* Rebased library changes + review changes

* Add more safety checks to extension accessors

* Remove instances where extension sets were unnecessarily allocated

* Remove cleared items from sets
Empty sets are now made null
IExtensionMessage -> IExtendableMessage

* Remove dead code from IExtensionValue impls

* Clean both repeated and single value extensions

* Add GetOrRegister method for repeated fields and allow clearing repeated extensions

* Add type safe ClearExtension methods, remove non-generic IExtendableMessage interface.

* Simplify ExtensionSet.TryMergeFieldFrom

* Rebase on master to resolve conflicts

* Fix Makefile.am

* Add ObjectIntPair to Makefile.am

Some compilers, such as PS4's clang, were giving errors such as:
C:\dev\protobuf\src\google/protobuf/parse_context.h(227,5): error : no type named 'uintptr_t' in namespace 'std'; did you mean simply 'uintptr_t'?
Adding the necessary include for integer types fixes these.

One example is when using seccomp with PR_SET_TSC set to PR_TSC_SIGSEGV.

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Change update_version to update the generated codes too

Remove unused files from lite's pom.xml

Partially Revert "Replaced all instances of Simple{IDF}toa with StrCat."

This reverts commit 029f2c7c.

* Add a new conformance test for top level JSON null

Replaced all instances of Simple{IDF}toa with StrCat.

Update the version for JavaLite in update_version script

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Down Integration to GitHub

This makes for easier rewrites between internal and external.

All bazel crosstools automatically pass -Wall to compiles. The order of
operations is:

- bazel crosstool flags
- `--host_copt` flags and other variations like `--host_cxxopt`
- the `copts` defined on the rule

Because of this when protobuf produces warnings, there's no way to
disable them from the consumer side if they are re-enabled later by
another `-Wall` flag.

These were found attempting to enable -Werror

GCC 8 added a -Wclass-memaccess that is enabled in -Wall that warns when
making direct memory modifications to non-trivial objects. The objects
that are modified here are only "non-trivial" in non-interesting ways
(e.g., removal of copy constructor) and can be safely modified as is
being done.

This simply explicitly casts the pointers before calling memset to
indicate that they should be treated as raw memory.

Down integrate to GitHub

Remove Required.Proto3.JsonInput.EmptyFieldMask.JsonOutput from failure list since it is now passing for Ruby

Replace SimpleItoa with StrCat in ObjectiveC compiler codes