Use std::shared_ptr instead of std::unique_ptr for Platform::TimerRef.

We currently support MSVC 2013, and MSVC 2013 has weird bugs around
std::unique_ptr; the one we hit is Connect ID 858243. You can't
actually open the bug report anymore because Microsoft has shut down
Microsoft Connect. We probably shouldn't support a compiler so old
its bugtracker doesn't exist anymore, but there isn't any very good
reason to use unique_ptr for TimerRef either, so let's change that
for the time being.

src/platform/gui.h

@@ -140,7 +140,7 @@ public:
     virtual void RunAfterProcessingEvents() { RunAfter(0); }
 };
 
-typedef std::unique_ptr<Timer> TimerRef;
+typedef std::shared_ptr<Timer> TimerRef;
 
 TimerRef CreateTimer();
 

src/platform/guigtk.cpp

@@ -218,7 +218,7 @@ public:
 };
 
 TimerRef CreateTimer() {
-    return std::unique_ptr<TimerImplGtk>(new TimerImplGtk);
+    return std::make_shared<TimerImplGtk>();
 }
 
 //-----------------------------------------------------------------------------

src/platform/guimac.mm

@@ -187,7 +187,7 @@ public:
 };
 
 TimerRef CreateTimer() {
-    return std::unique_ptr<TimerImplCocoa>(new TimerImplCocoa);
+    return std::make_shared<TimerImplCocoa>();
 }
 
 //-----------------------------------------------------------------------------

src/platform/guinone.cpp

@@ -89,7 +89,7 @@ public:
 };
 
 TimerRef CreateTimer() {
-    return std::unique_ptr<Timer>(new TimerImplDummy);
+    return std::make_shared<TimerImplDummy>();
 }
 
 //-----------------------------------------------------------------------------

src/platform/guiwin.cpp

@@ -258,7 +258,7 @@ public:
 };
 
 TimerRef CreateTimer() {
-    return std::unique_ptr<TimerImplWin32>(new TimerImplWin32);
+    return std::make_shared<TimerImplWin32>();
 }
 
 //-----------------------------------------------------------------------------