of MSVC

We *really* need these sorted out. I'd prefer to have them all removed and
the actual code corrected instead of just diabling the warnings and pretending
that they don't exist.

of compiler warnings, but I guess they make the life somewhat easier to live
for a ms dude compiling this. For a rainy day: remove the pragmas and correct
the source code that cause the warnings!

win32 systems

files depend on that as well. It turned out Borland has no unistd.h file
either, only mingw32 seems to use that.

HAVE_UNISTD_H is now not set if VC6 is defined