help the compiler create more efficient code

Patch from Michael <virtual_worlds@gmx.de>
Full text: As usual I have modified only minor things to remove warnigs when compiled as C++ code, have added some const-specifiers where possible to help the compiler create more efficient code and added some static-specifiers to make functions invisible to other modules.

backend/emf.c

@@ -35,6 +35,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <math.h>
+#include <malloc.h>
 #include "common.h"
 #include "emf.h"