Initialize crash handler in unit tests

This way, we don't get locking failures when we hit an assertion in
the unit tests.  Also, we might find out about unit test bugs from
folks who can't do gdb.

changes/crash_handler_in_tests

@@ -0,0 +1,3 @@
+  o Minor features:
+    - Enable the backtrace handler (where supported) when running the
+      unit tests.

src/test/test.c

@@ -43,6 +43,7 @@ long int lround(double x);
 double fabs(double x);
 
 #include "or.h"
+#include "backtrace.h"
 #include "buffers.h"
 #include "circuitlist.h"
 #include "circuitstats.h"
@@ -1379,6 +1380,7 @@ main(int c, const char **v)
   options = options_new();
   tor_threads_init();
   init_logging();
+  configure_backtrace_handler(get_version());
 
   for (i_out = i = 1; i < c; ++i) {
     if (!strcmp(v[i], "--warn")) {