Determine content_type with file command's --mime-type when content_type is not…

Determine content_type with file command's --mime-type when content_type is not found in the default cases.
(cherry picked from commit 2ca52df1)

lib/paperclip/upfile.rb

@@ -15,7 +15,8 @@ module Paperclip
       when %r"html?"                 then "text/html"
       when "js"                      then "application/js"
       when "csv", "xml", "css"       then "text/#{type}"
-      else "application/x-#{type}"
+      else
+        Paperclip.run("file", "--mime-type #{self.path}").split(':').last.strip rescue "application/x-#{type}"
       end
     end
 

test/upfile_test.rb

@@ -23,6 +23,14 @@ class UpfileTest < Test::Unit::TestCase
 
         assert_equal content_type, file.content_type
       end
+
+      should "return a content_type of text/plain on a real file whose content_type is determined with the file command" do
+        file = File.new(File.join(File.dirname(__FILE__), "..", "LICENSE"))
+        class << file
+          include Paperclip::Upfile
+        end
+        assert_equal 'text/plain', file.content_type
+      end
     end
   end
 end