Improve the data value fix-up step.

This resolves #534 by handling the case where data is a string, whether
it is provided alone or as a pair.  We can also eliminate the old and
unnecessary check for undefined values.
Remove unnecessary numeric value checks.

The previous processing step already guarantees that the values are
numeric.
Cache the data value, since it is used repeatedly.
Remove unnecessary debugging code.

Modern browser consoles obviate the need for an object logging function.
Updated credits for #534 pie string data fix.