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/login.c

@@ -43,9 +43,6 @@
 #include <unistd.h>
 #endif
 
-int expect(int s, int match, s_char *buf);
-void sendcmd(int s, int cmd, s_char *arg);
-
 int
 login(int s, s_char *uname, s_char *cname, s_char *cpass, int kill_proc)
 {