add all.h and use in place of diablo.h (#2005)

Now diablo.h is treated in the same way as all other header files of
Source, as it only contains the declarations of global variables and
functions of diablo.cpp.

Besides consistency, this also enables mods to include diablo.h just
like any other header file without having to include every header file
(and without having to include C++ specific aspects of the now all.h).

Source/dthread.cpp

@@ -1,4 +1,4 @@
-#include "diablo.h"
+#include "all.h"
 #include "../3rdParty/Storm/Source/storm.h"
 
 #ifdef __cplusplus