Revert "Fix C extension build warnings"

This reverts commit 03a8697866.

Turns out there was a good reason for this: it makes Overviewer work on
Debian. Why? Who knows. It's a mystery.

overviewer_core/src/overviewer.h

@@ -33,7 +33,7 @@
 
 // increment this value if you've made a change to the c extesion
 // and want to force users to rebuild
-#define OVERVIEWER_EXTENSION_VERSION 55
+#define OVERVIEWER_EXTENSION_VERSION 54
 
 /* Python PIL, and numpy headers */
 #include <Python.h>
@@ -42,6 +42,11 @@
 /* Fix Pillow on mingw-w64 which includes windows.h in Imaging.h */
 #undef TRANSPARENT
 
+/* like (a * b + 127) / 255), but much faster on most platforms
+   from PIL's _imaging.c */
+#define MULDIV255(a, b, tmp)								\
+	(tmp = (a) * (b) + 128, ((((tmp) >> 8) + (tmp)) >> 8))
+
 /* macro for getting a value out of various numpy arrays the 3D arrays have
    interesting, swizzled coordinates because minecraft (anvil) stores blocks
    in y/z/x order for 3D, z/x order for 2D */