Remove date.h and patchlevel.h from win/tty/wintty.c, win/X11/winX.c,
and sys/share/pcmain.c (caveat: the latter two are untested) so that they
don't get recompiled every time any other source file changes and triggers
creation of a new date.h. Only version.c needs to be recompiled in that
situation. Also, Makefile.src was missing a reference to botl.h.