Adding cropping support to rmagick processor

Signed-off-by: rick <technoweenie@gmail.com>

lib/technoweenie/attachment_fu/processors/rmagick_processor.rb

@@ -42,6 +42,9 @@ module Technoweenie # :nodoc:
           if size.is_a?(Fixnum) || (size.is_a?(Array) && size.first.is_a?(Fixnum))
             size = [size, size] if size.is_a?(Fixnum)
             img.thumbnail!(*size)
+          elsif size.is_a?(String) && size =~ /^c.*$/ # Image cropping - example geometry string: c75x75
+            dimensions = size[1..size.size].split("x")
+            img.crop_resized!(dimensions[0].to_i, dimensions[1].to_i)
           else
             img.change_geometry(size.to_s) { |cols, rows, image| image.resize!(cols<1 ? 1 : cols, rows<1 ? 1 : rows) }
           end