Add CuckooCache implementation and replace the sigcache map_type with it

SQUASHME: Change cuckoocache to only work for powers of two, to avoid mod operator
SQUASHME: Update Documentation and simplify logarithm logic
SQUASHME: OSX Build Errors
SQUASHME: minor Feedback from sipa + bluematt
SQUASHME: DOCONLY: Clarify a few comments.

src/test/test_bitcoin.cpp

@@ -19,6 +19,7 @@
 #include "ui_interface.h"
 #include "rpc/server.h"
 #include "rpc/register.h"
+#include "script/sigcache.h"
 
 #include "test/testutil.h"
 
@@ -39,6 +40,7 @@ BasicTestingSetup::BasicTestingSetup(const std::string& chainName)
         ECC_Start();
         SetupEnvironment();
         SetupNetworking();
+        InitSignatureCache();
         fPrintToDebugLog = false; // don't want to write to debug.log file
         fCheckBlockIndex = true;
         SelectParams(chainName);