aprintf() returns a const char *; the assignment to char * caused both
clang and gcc to warn of the dropped const.
Commit 893471a introduced a tiny memory leak, because GetFile()
stopped freeing buf. The const return type of aprintf() suggests that
the buffer must not be freed.
Now use Malloc() to allocate the buffer and free() to free it. This
also checks if we are out of memory, because Malloc() does the check
and aprintf() currently doesn't.
