Add mostly-static checks on consistency of Equihash parameters, MAX_HEADERS_RESULTS, and MAX_PROTOCOL_MESSAGE_LENGTH.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

src/gtest/test_block.cpp

@@ -0,0 +1,13 @@
+#include <gtest/gtest.h>
+
+#include "primitives/block.h"
+
+
+TEST(block_tests, header_size_is_expected) {
+    // Dummy header with an empty Equihash solution.
+    CBlockHeader header;
+    CDataStream ss(SER_NETWORK, PROTOCOL_VERSION);
+    ss << header;
+
+    ASSERT_EQ(ss.size(), CBlockHeader::HEADER_SIZE);
+}