THRIFT-1204: Ruby autogenerated files should require 'thrift' gem

THRIFT-1204: Ruby autogenerated files should require 'thrift' gem
Library: Ruby
Patch: Ilya Maykov
This patch does 2 things:
1) Adds a "require 'thrift'" line to the *_types.rb and *_constants.rb files,
   to be consistent with *_service.rb which was generating the thrift require
   already.
2) Adds a "rubygems" option to the --gen rb compiler target. When this option
   is specified, the compiler will add a "require 'rubygems'" line to the top
   of each gen-rb file. Defaults to false.

git-svn-id: https://svn.apache.org/repos/asf/thrift/trunk@1294949 13f79535-47bb-0310-9956-ffa450edef68