Various changes suggested by cppcheck

- remove unused variables
- reduce the scope where it makes sense
- correct limits (did you know that strcat()'s last parameter does not
  include the \0 that is always added?)
- set some free()'d pointers to NULL

Source/Core/Common/MemArena.cpp

@@ -36,7 +36,7 @@ int AshmemCreateFileMapping(const char *name, size_t size)
 		return fd;
 
 	// We don't really care if we can't set the name, it is optional
-	ret = ioctl(fd, ASHMEM_SET_NAME, name);
+	ioctl(fd, ASHMEM_SET_NAME, name);
 
 	ret = ioctl(fd, ASHMEM_SET_SIZE, size);
 	if (ret < 0)