make it compile under MSN vc. Unfortunately it has a weird crash at boot :(

- Lots of indenting changes
- VC++ is strict with variadic macros
- VC++ does not accept unistd.h
- new interface for walltime
- VC++ does not seem to have support for integer overflow.
- VC++ defines YENV_REG?
- no access flags, x permissions ignored.
- new FindGMP supporting MPIR
- make horus optional (c++ is hard).

OPTYap/opt.init.c

@@ -20,7 +20,9 @@
 #define OPT_MAVAR_STATIC
 #include "Yatom.h"
 #include "YapHeap.h"
+#if HAVE_UNISTD_H
 #include <unistd.h>
+#endif
 #include <signal.h>
 #ifdef YAPOR
 #include "or.macros.h"