Fix setting method visibility on method wrapped with prepend
Fix setting method visibility on method wrapped with prepend

Ignore prepended modules when looking for already defined methods on a
class to set the visibility on.
[Fix GH-1834]

From: Dylan Thacker-Smith <Dylan.Smith@shopify.com>

git-svn-id: ab86ecd26fe50a6a239cacb71380e346f71cee7d@62725 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ruby/rubyspec,eregon/rubyspec,ruby/spec,nobu/rubyspec,nobu/rubyspec,ruby/spec,nobu/rubyspec,eregon/rubyspec,eregon/rubyspec,ruby/spec,ruby/rubyspec