Reinitialize state in between individual unit tests.

This changes the TestingSetup fixture to be per-unit-test rather than global.
Most tests don't need it, so it's only invoked in a few.

src/test/alert_tests.cpp

@@ -15,6 +15,8 @@
 #include "util.h"
 #include "utilstrencodings.h"
 
+#include "test/test_bitcoin.h"
+
 #include <fstream>
 
 #include <boost/filesystem/operations.hpp>
@@ -78,7 +80,7 @@
 }
 #endif
 
-struct ReadAlerts
+struct ReadAlerts : public TestingSetup
 {
     ReadAlerts()
     {