Allow building with VC2015:
* Ignore warning c4091: unnamed typedef enums (in Windows SDK 7.1a dbghelp.h).
* fix warnings c4302, c4311, and c4312 (trunkation or extending when casting from a 32 bit type to a 64 bit type or the other way around):
* VBuf docHandles are now unsigned longs instead of ints.
* Replace all explicit casts from unsigned long to handles (HANDLE, HWND) with UlongToHandle.
* Replace all explicit casts from handles (HANDLE, HWND) to unsigned long with HandleToUlong.
