Automated testing tweaks for ObjC

- Move the ObjC tests into the list and exclude them on linux, this will change
  where in the order they start, since they are longer, it will have other
  things run in parallel instead of them ending up last and taking the longest.
- Switch to the Xcode 7.3 image.
- Drop the use of xctool and stream line things through the full_mac_build.sh
  script. This means we end up with only one build script instead of two.
- Tweaks to the mac build script:
  - Make iOS Xcode version support explicit
  - Support Debug/Release only building
  - Change the OS X min parallel count to 2 to better deal with VMs.
- Split the travis ios tests into the two Xcode Configurations as the logs are
  choking travis.

Better support for using the proto library from a framework.

Add js/binary/encoder.js to js_EXTRA_DIST.

- Add generator constant for the default framework name.
- Add generator api for making the CPP symbol from the name.
- Add generator api to see if it is a bundled proto file.
- Output a CPP conditional and two imports for the core library headers.
- Add helper for generating the #import for file headers to deal with the
  framework imports.
- Add a reference from the unittests to a WKT to use that to inspect how
  imports generate.
- Update the podspec to define the CPP symbol and require pods 1.0 (or later).

Fixes https://github.com/google/protobuf/issues/1457

added missing closing bracket for _cmakedir_desc in cmake/install.cmake:88

Add protobuf:: namespace to installed targets

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.