Fix #3218

This reverts commit dcc8ffd9.

* Add conformance tests for explicit packed/unpacked fields

* Fix typo

* Update failure lists

* Update failure list

* Use enum class to make enum scoped

* compatibility tests between last released and the current version

This change adds the required loads to examples and zlib.
For full compatibility with --incompatible_load_{cc,java,proto}_rules_from_bzl,
we will need to roll gtest to a newer version.

Windows: expand path names on command line

* Add binary conformance test for default repeated fields

1) Both packed and unpacked encoding should be accepted for parsing.
2) Encode should follow the default way for the syntax.

* Uncomment test

* Remove is_primitive

* Add failed tests to failure lists.

* Add failed test to failure list

* Use binary format to specify expected value

Text format cannot distinguish whether repeated field is packed or not.

* Change method name from ToHexString to ToOctString

* Add failed test to failure list

* Add failed test to php's failure list

* Fix comments

* Add csharp compatibility tests for 3.7.0

* Add compatibility test between last major version with current for C#

* Update last version number

* compatibility tests between last released and the current version

* fix typo

* support hashes for struct initalizers

* convert hash keys to string

* update tests

* add extra asserts

* Add binary conformance test for message type.

* Add test case for merge repeated scalar message field

* Add failed tests to failure list

* Add failed test to php's failure list

* Remove successful tests from php c's failure list

* Add binary conformance test for enum fields.

* Add failed conformance test to js failure list

* Add binary conformance test case for bytes field

* Add failed conformance test to php's failure list

https://github.com/matthew-brett/multibuild/pull/240

* Add conformance test for binary string

* Add failing tests to php failure list

https://github.com/matthew-brett/multibuild/pull/240

* Fix binary compatibility in FieldCodec factory messages

* Make default value parameter for current factories required

* Route old methods through default value overloads

Currently, if you access a ListValue from a Struct and attempted to
assign it to another Struct, you would get an exception:

   > s1 = spb.Struct()
   > s1['a'] = [1]
   > s2 = spb.Struct()
   > s2['a'] = s1['a']
   ValueError: Unexpected type

This fixes that case.

* Down integrate to GitHub

* Fix broken tests

I'm not exactly sure why, but this fixes the failing Bazel presubmit
test. Using the most recent version seems like a good idea anyway so
that we can make sure we're compatible with any new Bazel changes.

Since true for objc is external, changes should always start on the github
side, so the fact that something got pushed out is a sign something was
broken in the process.