Bug #1450: Illumos should be buildable with GCC4
libnisdb is inconsistently const-y
The sort-of-C++ code in libnisdb uses const inconsistently in a way which newer compilers notice.
It's a pain to fix fully, so as to minimize vexing casts, as after a certain point, the direction of vexing casts just changes (const off? const on?). I currently have changes which pacify compilers, and are somewhere close to the cost/benefit line.