thread.c: use the same method name

* thread.c (exec_recursive): use the same last method name as
  recursive_push in the error message when recursive_pop failed.
  [ruby-core:66742] [Bug #10579]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48752 b2dd03c8-39d4-4d8f-98ff-823fe69b080e