Only allow #extend to throw the error in Kernel#extend
Only allow #extend to throw the error in Kernel#extend

BanzaiMan/rubyspec,sgarciac/spec,eregon/rubyspec,kachick/rubyspec,wied03/rubyspec,ruby/rubyspec,ruby/spec,kachick/rubyspec,ruby/spec,kachick/rubyspec,eregon/rubyspec,wied03/rubyspec,ruby/rubyspec,nobu/rubyspec,wied03/rubyspec,nobu/rubyspec,BanzaiMan/rubyspec,ruby/spec,sgarciac/spec,sgarciac/spec,nobu/rubyspec,eregon/rubyspec