Upgrade gdtoa.tgz.
Update 'real' and 'real-int' regression output.

Older versions of gdtoa.tgz sometimes produced too many digits for
float/Real32 to string conversions.
Rename "Real<N>.strto" helper function to "Real<N>.strtor".

Rename to match gdtoa.tgz function.
Merge pull request #30 from MatthewFluet/gdtoa-upgrade

Upgrade gdtoa.tgz.