Add 'image/pjpeg' format used by IE

http://msdn.microsoft.com/en-us/library/ms775147%28v=vs.85%29.aspx#_replace

actionpack/lib/action_dispatch/http/mime_types.rb

@@ -9,7 +9,7 @@
 Mime::Type.register "text/csv", :csv
 
 Mime::Type.register "image/png", :png, [], %w(png)
-Mime::Type.register "image/jpeg", :jpeg, [], %w(jpg jpeg jpe)
+Mime::Type.register "image/jpeg", :jpeg, [], %w(jpg jpeg jpe pjpeg)
 Mime::Type.register "image/gif", :gif, [], %w(gif)
 Mime::Type.register "image/bmp", :bmp, [], %w(bmp)
 Mime::Type.register "image/tiff", :tiff, [], %w(tif tiff)