Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Merge gdtoa-20110304.

Add required header for isalnum(3) to quench compiler warnings

Forgotten in: r174678
Submitted by: Alexander Best alexbestms at wwu.de
Approved by: das

Some changes the vendor didn't want:

- Accept the '0x' prefix so strtod("nan(0x...)", NULL) returns the same
thing as gcc's builtin nan("0x...") for such strings.
- Don't return uninitialized memory.
- Finish processing the string up to the closing ')' (provided it's
lexically valid) for compatibility with C99 and *scanf().

This commit was generated by cvs2svn to compensate for changes in r165743,
which included commits to RCS files with non-trunk default branches.

Import of the latest gdtoa sources, which include fixes for minor
problems relating to NaNs and rounding.

Initial import of David Gay's gdtoa library for conversion between
strings and floating point.