* PHP: support 7.0

* Also fix in test_util.php

[skip ci]

Change-Id: I1ba6f6372a08b5796570851336e1a548602f60da

Change-Id: I3ff47358e66965cab34736eed2a477ae29f02f61

`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.

This is necessary so that the CMake build knows to include this header
file in the installation include/ directory.

Currently deserialization of a non-packed binary repeated field is quadratic in
the number of elements, because each time we parse a new element we copy over
all elements we have parsed so far. This CL fixes the performance problem by
having the generated deserialization code just call addX() instead of using
getX() and setX().

gson 2.3 has internal bug that it doesn't work with some versions of maven.

Had to strip out some JSPB-format test code,
but also added some .proto test messages that
had been improperly stripped out.

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