Fixed Math.log2 for huge Bignums.
Fixed Math.log2 for huge Bignums.

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