Replace Language#find_by_filename with Pathname#language

lib/linguist/pathname.rb

@@ -4,6 +4,24 @@ module Linguist
       @path = path
     end
 
+    def basename
+      File.basename(@path)
+    end
+
+    def extname
+      if basename[0] == ?.
+        basename
+      elsif basename.include?('.')
+        File.extname(basename)
+      else
+        basename
+      end
+    end
+
+    def language
+      Language.find_by_extension(extname)
+    end
+
     def to_s
       @path.dup
     end