Resolve warnings on Windows

Appease the compiler by resolving some of the reported warnings,
including:

- Control paths that don't return.

- Potentially uninitialized variables.

- Unused local variables.

- Unreachable code.

- Type safety.

- Synchronize declarations with definitions for functions.

lib/roken/base64.c

@@ -93,7 +93,7 @@ base64_encode(const void *data, int size, char **str)
     }
     *p = 0;
     *str = s;
-    return strlen(s);
+    return (int) strlen(s);
 }
 
 #define DECODE_ERROR 0xffffffff