`System.identityHashCode` returns a hash that does not consider a
Message's values. This means two Messages with identical values will not
have identical hashCodes.

This patch uses the pattern from RubyMap to combine the hashCodes from
all values in a given message and produce a unique, consistent,
value-based hash.

Objc extensions tweaks

For the secondary dictionary, use a custom CFDictionary with integer keys to
avoid the NSNumber conversions.

Fix #2036 (Ruby `hash` broken for Messages with repeated fields.)

Fix erroneous comment regarding String.substring

Since Java 7, Strings produced with String.substring do not share byte arrays.

Some php engine implementation doesn't have return_value_ptr properly set. Explicitly use &return_value.

Merge 3.0.x into master

Update the ObjC version checks to support a min and current version.

- Capture the version used to generated.
- Check at compile time and runtime that generated code isn't from a newer
  version, also check that the min version required is also supported.
- Keep the old constants/macros/functions to special case the last version
  that was working so those generated sources still work until we decide
  otherwise.

This pull request includes two implementation: C extension and PHP
package. Both implementations support encode/decode of singular,
repeated and map fields.

Add https://metacpan.org/pod/Google::ProtocolBuffers::Dynamic

benchmarks: update readme.txt

Compatibility with the new version of Bazel.

Allow the JsonFormat.Parser to ignore unknown fields

Fix Win32 error messages on Unicode build

Generalize plugin support in Bazel Skylark rule

include std::find()

Update repo in Bazel build files to use googletest instead of the deprecated gMock

Objc any helpers

Global variable HOST_CFG is deprecated and will not be supported soon.

Fix error and add note about lossy issues

Cherry pick objc test changes into 3.0.x branch

Support the -Wassign-enum compiler flag.

The default behaviour of throwing an exception remains

Fix #2032 unused parameter 'deterministic'

- Capture the ObjC prefix used when generating the the file.
- Track the containing type on descriptors.
- Mark descriptors where the message class name got a suffix added to it.
- Expose a fullName property on Descriptors.
- Add helpers for packing/unpacking Any messages.
- Bump the ObjC runtime version number. Since we added methods and invoke them
  in the generated code, ensure the code is running against a matching version.
  Otherwise, someone could compile against headers, but run with a framework
  that is older and get unknown selector failures.  This should trip clearer
  messaging.

Fixes https://github.com/google/protobuf/issues/1674

Parameter deterministic is unused in
InternalSerializeWithCachedSizesToArray(), which generates unused
parameter warning in every message.

Fix #2071 replacing /bin/sh with bash when generates descriptor

Merge pull request #1884 from hochhaus/valueWriterFn