Extract MakeUnique into utilmemory.h

And use it to reduce chainparamsbase's direct reliance on util.h to
only args handling.

utilmemory.h can be replaced with <memory> once we move to C++14.

src/util.h

@@ -1,5 +1,5 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2017 The Bitcoin Core developers
+// Copyright (c) 2009-2018 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -20,11 +20,11 @@
 #include <sync.h>
 #include <tinyformat.h>
 #include <utiltime.h>
+#include <utilmemory.h>
 
 #include <atomic>
 #include <exception>
 #include <map>
-#include <memory>
 #include <set>
 #include <stdint.h>
 #include <string>
@@ -346,13 +346,6 @@ template <typename Callable> void TraceThread(const char* name,  Callable func)
 
 std::string CopyrightHolders(const std::string& strPrefix);
 
-//! Substitute for C++14 std::make_unique.
-template <typename T, typename... Args>
-std::unique_ptr<T> MakeUnique(Args&&... args)
-{
-    return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
-}
-
 /**
  * On platforms that support it, tell the kernel the calling thread is
  * CPU-intensive and non-interactive. See SCHED_BATCH in sched(7) for details.