Fix C tests: pass DBL_MIN as likelihood_threshold instead of old precision value

The ancestor_matcher2_alloc signature changed from precision (int) to
likelihood_threshold (double) in e272b1e, but the test helper still
passed 14 (the old precision). This caused 8 matcher tests to fail.

Author: jeromekelleher

lib/tests/tests.c

@@ -1124,7 +1124,8 @@ run_match(const tsk_treeseq_t *ts, double rho, double mu, const allele_t *h,
     ret = matcher_indexes_alloc(&mi, ts->tables, NULL, 0);
     CU_ASSERT_EQUAL_FATAL(ret, 0);
     /* matcher_indexes_print_state(&mi, stdout); */
-    ret = ancestor_matcher2_alloc(&am, &mi, recombination_rate, mutation_rate, 14, 0);
+    ret = ancestor_matcher2_alloc(
+        &am, &mi, recombination_rate, mutation_rate, DBL_MIN, 0);
     CU_ASSERT_EQUAL_FATAL(ret, 0);
 
     ret = ancestor_matcher2_find_path(