Vendor redis_rb from Rubygems, not GitHub

Also just include the entire gem. Space used is negligible and this
way we don't have to think about what to leave in/out.

Create a vendor-gem script in Ruby instead of Make.

lib/vendor/redis/test/support/connection/hiredis.rb

+require "support/wire/thread"

lib/vendor/redis/test/support/connection/ruby.rb

+require "support/wire/thread"

lib/vendor/redis/test/support/connection/synchrony.rb

+require "support/wire/synchrony"
+
+module Helper
+  def around
+    rv = nil
+
+    EM.synchrony do
+      begin
+        rv = yield
+      ensure
+        EM.stop
+      end
+    end
+
+    rv
+  end
+end