I got a patch from someone who uses nvpair code outside of illumos. It fixes a
couple of gcc warnings/bugs for him.
   1. silence uninitialized use warnings
   2. add parentheses around assignment used as truth value
   3. fix printf format specifier (ll is for integers only)
   4. strstr, strspn, strcspn, and strcmp are declared in string.h, not
      strings.h.
   5. avoid scanning integer into boolean variable