Don't return a version that equals the basename

Return nil instead

Library/Homebrew/pathname+yeast.rb

@@ -128,6 +128,8 @@ class Pathname
     stem.scan /_([^_]+)/ do |match|
       return match.first if /\d/.match $1
     end
+
+    nil
   end
 end
 

Library/Homebrew/unittest.rb

@@ -196,6 +196,11 @@ class BeerTasting <Test::Unit::TestCase
     end
   end
   
+  def test_no_version
+    assert_nil Pathname.new("http://example.com/blah.tar").version
+    assert_nil Pathname.new("arse").version
+  end
+  
   def test_bad_version
     assert_raises(RuntimeError) {f=TestBadVersion.new}
   end