Load comctl32.dll (for drag lists) at run time.

This too is not in the list of known DLLs on Windows 10. I don't know
of any actual viable hijacking attack based on it, which according to
my reading of MSDN (specifically, a rather vague hint in
https://msdn.microsoft.com/library/ff919712) _may_ be because we
mention the common controls assembly in our application manifest; but
better safe than sorry.

Now the entire list of remaining DLLs that PuTTY links against at load
time is a subset of the Win10 known DLLs list, so that _should_ mean
that everything we load before we've deployed our own defence
(SetDefaultDllDirectories) is defended against for us by Windows
itself.

windows/window.c

@@ -359,7 +359,7 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
 
     sk_init();
 
-    InitCommonControls();
+    init_common_controls();
 
     /* Set Explicit App User Model Id so that jump lists don't cause
        PuTTY to hang on to removable media. */