Review request for JDK-8010803: Number to String conversion functionality overhaul

[Hannes Wallnoefer]

Please review JDK-8010803: Number to String conversion functionality 
overhaul:

http://cr.openjdk.java.net/~hannesw/8010803/

This is a mostly complete port of the V8 double conversion code[1] to 
Java. It includes Bignum-based algorithms for converting doubles to 
shortest, precision, and fixed decimals representation, as well as 
specialized faster algorithms for each of the conversion modes.

The only thing I left out is string to number conversion and support for 
single precision floats, both of which is not needed for Nashorn. I also 
ported all the relevant tests, which includes 100,000 random numbers for 
each of the (shortest|precision|fixed) conversion modes as well as well 
as unit tests for various implementation classes.

With this new dtoa conversion we are fully compatible with all other JS 
implementations. The fast algorithms are also about 5x faster than what 
we had before. The fallback Bignum implementation still roughly provides 
a 2x speedup.

[1]: https://github.com/google/double-conversion

Thanks,
Hannes