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/or.cow_engine.c

@@ -18,7 +18,9 @@
 #include "Yap.h"
 #ifdef YAPOR_COW
 #include <sys/types.h>
+#if HAVE_UNISTD_H
 #include <unistd.h>
+#endif
 #include <stdio.h>
 #include "Yatom.h"
 #include "YapHeap.h"