Merge upstream fix to eliminate build-breaking gcc warnings of no
importance.

commit: cab33b7a0acba7d2268a23c4383be6167106e549

Update ND_TTEST2 to fix issue 443

Add IS_NOT_NEGATIVE macro.
Avoid these warnings:

• comparison of unsigned expression >= 0 is always true [-Wtype-limits],
• comparison is always true due to limited range of data type [-Wtype-limits].

Approved by: jmallett (mentor)