[#290] Adding rmagick, making it opt-out

using version < 2.0 since later versions do not work w/o backports on Debian Lenny

Gemfile

@@ -16,6 +16,10 @@ group :openid do
   gem "ruby-openid", '~> 2.1.4', :require => 'openid'
 end
 
+group :rmagick do
+  gem "rmagick", "~> 1.15.17"
+end
+
 # Use the commented pure ruby gems, if you have not the needed prerequisites on
 # board to compile the native ones.  Note, that their use is discouraged, since
 # their integration is propbably not that well tested and their are slower in