Make BigDecimal::limit work for subtraction and division. Fix jruby/jruby#1615.
Make BigDecimal::limit work for subtraction and division. Fix jruby/jruby#1615.

ruby/spec,ruby/rubyspec,ruby/spec,ruby/spec,eregon/rubyspec,eregon/rubyspec,nobu/rubyspec,eregon/rubyspec,ruby/rubyspec,nobu/rubyspec,nobu/rubyspec