Support UTF-8 encoded Unicode for user communications.

(NF_UTF8, togg): New client flag.
(flash, wall): User text input filtering.
(parse, prmptrd): Normal text input filtering.
(uprmptrd, ugetstring): New, to get user text.
(getele, flash, wall): Use them.
(getele): No need to filter out funny characters; input filtering
takes care of them.
(sendmessage, ufindbreak): Work on user text.
(uprnf): New, to print user text.
(rea, gamedown, show_motd): Use it.
(prnf): Unused, remove.
(pr, upr_player): Normal text output filtering (with highlighting).
(pr_flash): User text output filtering.

include/nat.h

@@ -172,5 +172,7 @@ extern void agecontact(struct natstr *np);
 #define NF_SONAR	bit(4)	/* Turn auto-sonar on */
 #define NF_TECHLISTS    bit(5)	/* Sort lists by tech not type */
 #define NF_SACKED       bit(6)	/* Capital was sacked, and hasn't been reset yet */
+#define NF_UTF8         bit(7)	/* Whether the client accepts UTF-8 (true) or
+                                   ASCII only (false) */
 
 #endif /* _NAT_H_ */