git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@17842 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
FIXNUM_MAX to make it possible to convert to double accurately.
It assumes FLT_RADIX is 2.
fix RubyForge bug #14102.
backported from 1.9.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@17842 b2dd03c8-39d4-4d8f-98ff-823fe69b080e