Removed the HAVE_STRERROR directive and our replacement strerror() function for ...

Removed the HAVE_STRERROR directive and our replacement strerror() function for 'systems which don't have strerror()'.  Seriously, people, it's 2016 and *every* system has strerror.  Linux has it.  FreeBSD has it.  Mac OS has it.  Even the vaguely unix-like OpenBSD has it.  Maybe this was put in to support Tru64 or some other long-gone extinct unix, but at this point there is no longer any point in duplicating functionality which we can confidently guarantee will be in the standard C library of any usable operating system.