* include/ruby/ruby.h (POSFIXABLE): use FIXNUM_MAX+1 instead of
	  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_7@17989 b2dd03c8-39d4-4d8f-98ff-823fe69b080e