Fix warnings and 64-bit problems in openbsd-malloc code
The warning fixes are: - Only define issetugid if it's missing. - Explicitly ignore the return value of writev. - Explicitly cast the retval of readlink() to int. The 64-bit problems are related to just storing a size_t in an int. Not cool! Use a size_t instead. Fix for bug 6379. Bugfix on 0.2.0.20-rc, which introduced openbsd-malloc.