[bind10-dev] wiki page update on "if (ptr)" vs "if (ptr != NULL)"

[JINMEI Tatuya / 神明達哉]

In a recent code review discussion I realized we didn't update the
coding guideline wiki page on this matter (we decided to change it
several months ago), so I now updated it:
http://bind10.isc.org/wiki/CodingGuidelines#NULLpointercheck

Feel free to correct any minor errors directly or add minor missing
points.  If there's a substantial error please point it out here.

---
JINMEI, Tatuya