find.rb: add ignore_error

* lib/find.rb (Find#find): add "ignore_error" keyword argument
  defaulted to true.  [ruby-core:51025] [Feature #7596]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45241 b2dd03c8-39d4-4d8f-98ff-823fe69b080e