Declare tags.c variables in tags.h. Declare stuff with external

linkage that is not in any other header in misc.h.  Remove some
redundant declarations elsewhere.
(prompt, doredir, dopipe, doexecute, output, screen, parsedelay):
Static linkage.

src/client/expect.c

@@ -142,7 +142,6 @@ expect(int s, int match, s_char *buf)
 void
 sendcmd(int s, int cmd, s_char *arg)
 {
-    extern struct fn fnlist[];
     s_char buf[128];
     int cc;
     int len;