common, pay: actually test Dijkstra and route finding.

Set up a simple line of channel pairs, where one should be preferred
over the other for our various reasons.  Make sure this works, both
using a low-level call to Dijkstra and at a higher level as the pay
plugin does.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/dijkstra.c

@@ -1,5 +1,7 @@
 /* Without this, gheap is *really* slow!  Comment out for debugging. */
+#ifndef TESTING
 #define NDEBUG
+#endif
 #include "config.h"
 #include <ccan/cast/cast.h>
 #include <common/dijkstra.h>

plugins/test/Makefile

@@ -22,6 +22,13 @@ plugins/test/run-route-overlong:		\
 	common/node_id.o			\
 	common/route.o
 
+plugins/test/run-route-calc:			\
+	common/fp16.o				\
+	common/gossmap.o			\
+	common/node_id.o			\
+	common/route.o				\
+	gossipd/gossip_store_wiregen.o
+
 $(PLUGIN_TEST_PROGRAMS): $(BITCOIN_OBJS) $(WIRE_OBJS) $(PLUGIN_TEST_COMMON_OBJS)
 
 $(PLUGIN_TEST_OBJS): $(PLUGIN_FUNDER_HEADER) $(PLUGIN_FUNDER_SRC)