Support for files generated by Racc.

This changeset includes a sample racc file from [this auto-generated
file](44e9bf0440/lib/rjson/parser.rb)
(MIT-licensed).

[Racc](https://github.com/tenderlove/racc) Racc is an LALR(1) parser
generator. It is written in Ruby itself, and generates ruby programs.

test/test_blob.rb

@@ -255,6 +255,9 @@ class TestBlob < Minitest::Test
 
     # Unity3D-generated metadata
     assert sample_blob("Unity3D Asset/Tiles.meta").generated?
+
+    # Racc-generated Ruby
+    assert sample_blob("Ruby/racc.rb").generated?
   end
 
   def test_vendored