Performance enhancements:

Performance enhancements:

1. Changed DRAGON4-FIXUP to use fast scaling similar to described in
   Burger and Dybvig (reference in file).  This makes an order of
   magnitude difference for unparsing flonums with large exponents.

2. Changed DRAGON4 to pass exponent to DRAGON4-FIXUP for scaling
   estimate.

3. Systematically replaced calls to generic operators with calls to
   int: variants (and rat:expt).  The vast majority of operations are
   on bignums.  Gives a gain of about 20%.

Timings (Non-GC runtime) in msec for 1000 calls on 200Mhz Pentium Pro.

	Example Number		Original	Fast Scaling	and INT:ops

	3.141592653589793	840		820		580
	1022.			320		300		230
	1.234e300		4870		490		400
	1.23456e-300		7130		680		540

It is still pretty sad that you can format only a few thousand numbers
per second.

PC-sampling shows that most of the time is spent as follows:

 (27% primitive 253 "INTEGER-MULTIPLY")
 (24% primitive 200 "GARBAGE-COLLECT")
 (24% primitive 248 "INTEGER-DIVIDE")
 (5%. primitive 260 "INTEGER-SUBTRACT")