Update Ruby gem version to 3.0.0.alpha.2.0.

This update conforms to our two-numbers-after-alpha scheme that allows
us to bump the last number if we need to re-upload a gem. (Rubygems does
not allow re-use of a version number once a gem is uploaded.)

Change-Id: Ia8e7c129d19800afd66f8052785cf5a00462c7ba

Updated CHANGES.txt to mention Ruby extension.

Change-Id: I8c3717f549c9b4e9d07c77ec5875c9cd62b296ac

Change-Id: I3c3ec4aecf4ea2ce786d8d674baeca875e71801f

Change-Id: I4cbb3374e351c31611de472c7d5d78e4ce2b0f3b

pass in systems without rtti.

Change-Id: Ib32b47a66f14928de9399c49dbdb07263a30d1bc

Change-Id: I6a51a35c69ac24a60dd96ef69d556b1e68bc37d6

Change-Id: Iafd4a3aa9d55e31478bf070311eeadfe95ece4d7

Use EMPTY_BYTES in WireFormatNano

Integrated changes from Google opensource branch.

Implement maps for JavaNano

Ruby implementation Map#inspect should be consistent with Hash#inspect

Properly support maps in Ruby protoc and another bugfix.

Previously, we supported map fields in the Ruby DSL. However, we never
connected the final link in the chain and generated `map` DSL commands
for map fields in `.proto` files. My apologies -- I had been testing
with the DSL directly so I missed this.

Also fixed a handlerdata-setup-infinite-loop when a map value field's
type is its containing message.

MIPS: remove immediate constraint within CompareAndSwap.

Add java compiled targets and several tests target into .gitignore.

Improper use of immediate constraint is slightly non-optimal with gcc/gnu-as
but may cause breakage with clang.