unpack.m: Stop hang when unpacking on to existing filename (bug #45331). * unpack.m: Follow documentation and use current directory for unpacking if no output directory is specified. Call tilde_expand() on any user-supplied directory in case it contains '~'. Add -f(orce) flag to gzip and bzip unpack commands so that any file will be overwritten and Octave will not hang waiting for user input. Strip trailing file separator from output directory so that a proper comparison is made to beginning directory which never includes the file separator.

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