Users often encounter a Python import error when trying to build Python
protos if protobuf is installed locally on the machine. In this case,
Python ends up looking in the wrong directory when importing files (see
bazelbuild/bazel#1209 and tensorflow/tensorflow#2021). It seems that the
problem is caused by Python getting confused when there are Python
source files that are meant to be part of the same package but are
in separate directories.

Prior to #1233, the Bazel build setup would copy the Python
runtime sources and all generated sources for the builtin protos into
the root directory (assuming that the protobuf tree is vendored in a
google/protobuf directory).

With #1233, the two sets of sources are kept in their respective
directories but both `src/` and `python/` are added to the `PYTHONPATH`
using the new `imports` attribute of the Bazel Python rules. However,
both the runtime sources and the generated sources are under the same
package: `google.protobuf`, causing Python to become confused when
trying to import modules that are in the other directory.

This patch adds a workaround to the Bazel build to add a modified
version of the original `internal_copied_filegroup` macro to copy the
`.proto` files under `src/` to `python/` before building the
`py_proto_library` targets for the builtin protos. This ensures that the
generated sources for the builtin protos will be in the same directory
as the corresponding runtime sources.

This patch was tested with the following:
* All Python tests in protobuf
* All Python tests in tensorflow
* All tests in [Skydoc](https://github.com/bazelbuild/skydoc)
* Importing protobuf as `//google/protobuf`
* Importing and binding targets under `//external`
* Importing protobuf as `//third_party/protobuf`

Add compatibilty tests against v2.5.0

Make the CocoaPods integration tests more robust

Make protobuf-config-version.cmake.in set the required variables

Make cmake configuration file install path configurable

- Env solution doesn't seem to always work, use template pod files and copy
  them in place instead.
- Flush the pods cache before and after runs.
- Make pod install verbose to have the info incase something goes wrong.

Update protobuf-config-version.cmake.in to correctly set the required variables (PACKAGE_VERSION_EXACT, PACKAGE_VERSION_COMPATIBLE, PACKAGE_VERSION_UNSUITABLE)

Fix the cmake configuration file install path to be more standards compliant (See the description of cmake's config search behavior on https://cmake.org/cmake/help/v3.4/command/find_package.html)

Add shared schemes for the CocoaPods integration tests

Otherwise the projects have to be opened once to create user schemes for the
command line builds to work.

OS X gitignore cleanup and cocoapods integration tests

- Add an Xcode 6.3 created default iOS Project.
- Add an Xcode 6.3 created default OS X Project.
- Add Podfiles to for both that use Protobufs from within the tree.
- Add a script to run the tests (and cleanup) to help confirm the state of the
  Protobuf.podspec and sources.

Ruby oneofs: return default instead of nil for unset fields.

- Add the folder CocoaPods will add to the root folder.
- Move and expand the entries in the objectivec directory.

Export class Arena to shared library.

Fix #include in js_generator.cc

Merge beta-3 release branch again.

Integrate interanl changes

JSON format for Any message must print @type first

Fix protoc artifact pom version

This got broken in commit 6ef984af
which integrated changes from internal branch.

The commit 3b3c8abb has replaced the <>
with "" in #include statement in js_generator.cc

Added download_url to be able to upload to pypi.

Merge Beta 3 release branch into master

Update changes for lite

Remove the comments about iterator validation

As it may be implementation dependent.

Update changelogs for C++ maps

Test redundant varint fields decoding in JS.

Remove the instructions for pbconfig.h