Fix msvc compiler error C4146 (unary minus operator applied to unsigned type)

On msvc14, int literal '-2147483648' is invalid, because '2147483648' is unsigned type and cant't apply minus operator to unsigned type.
To define the int literal correctly, use '-2147483647 - 1' formula that is also used to define INT_MIN in limits.h.

src/test/util_tests.cpp

@@ -321,7 +321,7 @@ BOOST_AUTO_TEST_CASE(test_ParseInt32)
     BOOST_CHECK(ParseInt32("1234", &n) && n == 1234);
     BOOST_CHECK(ParseInt32("01234", &n) && n == 1234); // no octal
     BOOST_CHECK(ParseInt32("2147483647", &n) && n == 2147483647);
-    BOOST_CHECK(ParseInt32("-2147483648", &n) && n == -2147483648);
+    BOOST_CHECK(ParseInt32("-2147483648", &n) && n == (-2147483647 - 1)); // (-2147483647 - 1) equals INT_MIN
     BOOST_CHECK(ParseInt32("-1234", &n) && n == -1234);
     // Invalid values
     BOOST_CHECK(!ParseInt32("", &n));