use median filter for peer-reported reported number of blocks

- fixes problem that one misconfigured or malicious node can mess up progress bar
- implementation in src/util.h
- testcase in src/test/util_tests.cpp

src/test/util_tests.cpp

@@ -0,0 +1,36 @@
+#include <vector>
+#include <boost/test/unit_test.hpp>
+#include <boost/foreach.hpp>
+
+#include "../util.h"
+
+using namespace std;
+
+BOOST_AUTO_TEST_SUITE(util_tests)
+
+BOOST_AUTO_TEST_CASE(util_MedianFilter)
+{    
+    CMedianFilter<int> filter(5, 15);
+
+    BOOST_CHECK(filter.median() == 15);
+
+    filter.input(20); // [15 20]
+    BOOST_CHECK(filter.median() == 17);
+
+    filter.input(30); // [15 20 30]
+    BOOST_CHECK(filter.median() == 20);
+
+    filter.input(3); // [3 15 20 30]
+    BOOST_CHECK(filter.median() == 17);
+
+    filter.input(7); // [3 7 15 20 30]
+    BOOST_CHECK(filter.median() == 15);
+
+    filter.input(18); // [3 7 18 20 30]
+    BOOST_CHECK(filter.median() == 18);
+
+    filter.input(0); // [0 3 7 18 30]
+    BOOST_CHECK(filter.median() == 7);
+}
+
+BOOST_AUTO_TEST_SUITE_END()