* vm_insnhelper.c (argument_error): insert dummy frame to make
  a backtrace object intead of modify backtrace string array.
  [Bug #9295]
* test/ruby/test_backtrace.rb: add a test for this patch.
  fix test to compare a result of Exception#backtrace with
  a result of Exception#backtrace_locations.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44411 b2dd03c8-39d4-4d8f-98ff-823fe69b080e