remove Class#alloc method
Merge branch 'master' of github.com:mruby/mruby
Merge branch 'master' of github.com:mruby/mruby
Merge branch 'master' of github.com:mruby/mruby
add Exception#backtrace
Merge branch 'get-backtrace' of https://github.com/wanabe/mruby into wanabe-get-backtrace
undef print_backtrace_i() unless ENABLE_STDIO
add cast to void*
do not use mrb_alloca() that keeps memory until mrb_state freed