extensions: prohibit unicode defaults If the default value of an option is a unicode string (something than happen easily when using a 'from __future__ import unicode_literals'), any value passed on the command line will be ignored because the fancyopts module only checks for byte strings and not unicode strings. Changing fancyopts behavior is easy but would make assumptions on how the python3 port should be done, which is outside the scope of this patch. The chosen approach is to stop an extension from being loaded when a unicode default value is detected, with a hint for the developer.