Use #to_s on the geometry option in the Thumbnail processor.

This should make it possible to avoid passing a :geometry in the style
definition (when passing it as a hash), thus making Paperclip avoid resizing the
image. This is helpful when you want to perform your own custom
resizing/cropping using :convert_options rather than the default options offered
by Paperclip itself.

lib/paperclip/thumbnail.rb

@@ -28,7 +28,7 @@ module Paperclip
     def initialize(file, options = {}, attachment = nil)
       super
 
-      geometry             = options[:geometry] # this is not an option
+      geometry             = options[:geometry].to_s # this is not an option
       @file                = file
       @crop                = geometry[-1,1] == '#'
       @target_geometry     = options.fetch(:string_geometry_parser, Geometry).parse(geometry)