Add spec for backtrace from rescue that only captures $!.
Add spec for backtrace from rescue that only captures $!.

See jruby/jruby#4240

ruby/rubyspec,nobu/rubyspec,ruby/spec,eregon/rubyspec,sgarciac/spec,sgarciac/spec,eregon/rubyspec,ruby/rubyspec,kachick/rubyspec,eregon/rubyspec,nobu/rubyspec,ruby/spec,nobu/rubyspec,kachick/rubyspec,sgarciac/spec,ruby/spec,kachick/rubyspec