remove possibility of 63 bit overflow in ParseMoney

- also, add unit tests for various functions in util.cpp/util.h

src/test/test_bitcoin.cpp

@@ -10,6 +10,8 @@
 #include "transaction_tests.cpp"
 #include "DoS_tests.cpp"
 #include "base64_tests.cpp"
+#include "util_tests.cpp"
+#include "base58_tests.cpp"
 
 CWallet* pwalletMain;