Free allocated memory on exit

This should reduce the number of possible memory leaks reported by
valgrind. The remaining reported leaks are sched tqe allocation, async
DNS instance allocation, cmdmon response/timestamp cell allocation, and
clientlog subnet allocation.

sources.c

@@ -165,6 +165,7 @@ source_to_string(SRC_Instance inst);
 void SRC_Initialise(void) {
   sources = NULL;
   sort_list = NULL;
+  sel_sources = NULL;
   n_sources = 0;
   max_n_sources = 0;
   selected_source_index = INVALID_SOURCE;
@@ -183,6 +184,11 @@ void SRC_Finalise(void)
 {
   LCL_RemoveParameterChangeHandler(slew_sources, NULL);
   LCL_RemoveDispersionNotifyHandler(add_dispersion, NULL);
+
+  Free(sources);
+  Free(sort_list);
+  Free(sel_sources);
+
   initialised = 0;
 }