* vm.c (backtrace_object): remove lev and n parameter.
backtrace_object always returns all of backtrace information.
* vm.c (rb_backtrace_to_str_ary): fix to use backtrace_object().
This change improve performance of caller(lev, n).
* benchmark/bm_vm3_backtrace.rb: added to check above improvement.
FYI: measurement on my laptop, 1.9.3p229 needs 5.125 sec,
and current trunk only needs 0.299sec.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@35800 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
