(hap_req): New.

(nati, populace): Use it.

(populace, nati): Change hap, pct from float to double, because they
are used as double.

(nati): Print happiness needed with just two decimals, like the other
levels.

src/lib/common/hap_fact.c

@@ -62,3 +62,11 @@ hap_fact(struct natstr *tnat, struct natstr *vnat)
 	hap_fact = 0.8;
     return hap_fact;
 }
+
+/* Return happiness required to keep NP's citizens happy.  */
+double
+hap_req(struct natstr *np)
+{
+    return (np->nat_level[NAT_TLEV] - 40.0) / 40.0
+	+ np->nat_level[NAT_ELEV] / 3.0;
+}