Change default md5.h to use prototypes (#710)

Author: bernstei

src/libAtoms/md5.h

@@ -7,7 +7,7 @@
 The following makes PROTOTYPES default to 0 if it has not already  been defined with C compiler flags.
  */
 #ifndef PROTOTYPES
-#define PROTOTYPES 0
+#define PROTOTYPES 1
 #endif
 
 /* POINTER defines a generic pointer type */