Get rid of PARAMS macro usage.

It's 2013, no compiler still in use today needs this.
Compilers are better at vectorizing now.
Remove MS-DOS support.

All code within #ifdef __MSDOS__ has been removed.
Build fix after 'Compilers are better at...'
mmove() is just memmove()
mset() is just memset()
Remove code within #ifdef junk .. #endif
Assume openpty() exists
Remove Amiga support
Remove unused dir.c