Add tsearch and friends, and a test program

tsearch is missing from windows. use the netbsd version as it's
license-compatible.

lib/roken/version-script.map

@@ -139,6 +139,10 @@ HEIMDAL_ROKEN_1.0 {
 		rk_timevaladd;
 		rk_timevalfix;
 		rk_timevalsub;
+		rk_tdelete;
+		rx_tfind;
+		rk_tsearch;
+		rk_twalk;
 		rk_undumpdata;
 		rk_unvis;
 		rk_vasnprintf;