* Rolled forward again with "Updated upb from defcleanup branch..."

Revert "Revert "Updated upb from defcleanup branch and modified Ruby to use it (#5539)" (#5848)"

This reverts commit 1568deab.

* A few more merge fixes.

* Updated for defcleanup2 branch.

* Fixed upb to define upb_decode().

* Fixed names of nested messages.

* Revert submodule.

* Set -std=gnu90 and fixed warnings/errors.

Some of our Kokoro tests seem to run with this level of warnings,
and the source strives to be gnu90 compatible.  Enforcing it for
every build removes the possibility of some errors showing up in
Kokoro/Travis tests only.

* Fixed remaining warnings with gnu90 mode.

I tried to match warning flags with what Ruby appears to do
in our Kokoro tests.

* Initialize values registered by rb_gc_register_address().

* Fixed subtle GC bug.

We need to initialize this marked value before creating the instance.

* Truly fix the GC bug.

* Updated upb for mktime() fix.

* Removed XOPEN_SOURCE as we are not using strptime().

* Removed fixed tests from the conformance failure list for Ruby.

* Fixed memory error related to oneof def names.

* Picked up new upb changes re: JSON printing.

* Uncomment concurrent decoding test.

This changes to_time to use Ruby's built in Time.at with nanos support
rather than calculating a float and passing it to Time.at. The new
version runs about 3 times faster than the original version and
allocates fewer objects.

Warming up --------------------------------------
    protobuf#to_time    57.296k i/100ms
      faster#to_time   133.229k i/100ms
Calculating -------------------------------------
    protobuf#to_time    635.361k (± 2.1%) i/s -      3.209M in   5.052169s
      faster#to_time      1.873M (± 3.3%) i/s -      9.459M in   5.055169s

Comparison:
      faster#to_time:  1873368.8 i/s
    protobuf#to_time:   635361.4 i/s - 2.95x  slower

Calculating -------------------------------------
    protobuf#to_time   326.000  memsize (   126.000  retained)
                         7.000  objects (     2.000  retained)
                         0.000  strings (     0.000  retained)
      faster#to_time    86.000  memsize (     0.000  retained)
                         1.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)

Comparison:
      faster#to_time:         86 allocated
    protobuf#to_time:        326 allocated - 3.79x more

In general, I think it will help us to debug issues if we have less C
code and more Ruby code.  This method can be implemented in pure Ruby,
so this commit converts it to pure Ruby.

This reverts commit 37581380.

Revert "Revert "Enable the ignore_unknown_field option in the Ruby unmarshal options" (#5511)" (#5533)

* Revert "Revert "Enable the ignore_unknown_field option in the Ruby unmarshal options" (#5511)"

This reverts commit be1716a6.

* Separate ruby conformance test on Mac

* Fix shell syntax

* Fix test

This adds the ability for the MRI Ruby library to optionally pass in a
ignore_unknown_fields option when decoding JSON. The functionality was
added upstream in upb, this change exposes that option.

Given an argument, the previous implementation was off by one
(`.first(2)` would return 3 elements) compared to the `Enumerable#first`
method.

* This allows for ruby code to catch and handle Protobuf
    TypeErrors separately from the standard Ruby TypeError

  * Maintains backwards compatibility by having the new
    Google::Protobuf::TypeError inherit from the base
    TypeError. Any code that was catching TypeError should
    continue to work.

Make RepeatedField#delete_if consistent with Array#delete_if.

`.quo` return the most exact devision which fixes accuracy problems for the
timestamp coercion

This will allow loading the extension for Ruby 2.1.10...

This fixes the test_acts_likes_an_array test in RepeatedFieldTest, which
checks that repeated fields respond to the same methods as regular Ruby
arrays. The bsearch_index and dig array methods seem to be new in Ruby
2.3 and so we should support those.

Change-Id: If7b1cc0f03f609a7f43ddafc8509b44207c60910

This involved fixing a few important bugs in the
Ruby implementation -- mostly cases of mixing
upb field types and descriptor types (upb field
types do not distinguish between int/sint/fixed/sfixed
like descriptor types do).

Also added protobuf-specific exceptions so parse
errors can be caught specifically.

Change-Id: Ib49d3db976900b2c6f3455c8b88af52cfb86e036

* make consistent between mri and jruby
* create a #to_h and have it use symbols for keys
* add #to_json and #to_proto helpers on the Google::Protobuf message classes

starting to make `RepeatedField` quack like an array

additional changes:
* make sure gemspec gets all ruby code files
* add homepage in gem spec removes one of the warnings, and the gem spec authors are pushing
everyone to include a homepage in the gem
* remove excess whitespace in test suite to bring formatting inline with the rest of the file

system. The Ruby module build now uses an amalgamated distribution of
upb, and successfully builds a Ruby gem called 'google-protobuf' with
module 'google/protobuf'.