Rename all feature flags to HAVE_* and move out of makefiles into a configure

script which must be run before building.

Still two makefiles but they are a hell of a lot simpler.

HAVE_* also will make it easier to move to $buildsystem if necessary later.

window.c

@@ -1,4 +1,4 @@
-/* $Id: window.c,v 1.73 2009-05-04 17:58:27 nicm Exp $ */
+/* $Id: window.c,v 1.74 2009-05-13 23:27:00 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -28,23 +28,23 @@
 #include <termios.h>
 #include <unistd.h>
 
-#ifndef NO_PATHS_H
+#include "tmux.h"
+
+#ifdef HAVE_PATHS_H
 #include <paths.h>
 #endif
 
-#ifdef USE_LIBUTIL_H
+#ifdef HAVE_FORKPTY
+#ifdef HAVE_LIBUTIL_H
 #include <libutil.h>
-#else
+#endif
 #ifdef USE_PTY_H
 #include <pty.h>
-#else
-#ifndef NO_FORKPTY
+#endif
+#ifdef HAVE_UTIL_H
 #include <util.h>
 #endif
 #endif
-#endif
-
-#include "tmux.h"
 
 /*
  * Each window is attached to one or two panes, each of which is a pty. This