Fixed on the stable branch

• https://hg.savannah.gnu.org/hgweb/octave/rev/0dd5b293b18c

This will be part of Octave 5.2.

In Octave 4.4 and older, "pkg install foo.zip" worked.

This is related to bug #54657 and https://hg.savannah.gnu.org/hgweb/octave/rev/75ed70a1c108 fixing the 'unpack' function. I think that bug fix is entirely accurate, but it did not account for this regression in the 'pkg' function.

The 'pkg' subfunction 'install.m' uses the 'untar' function, regardless of the input file. This used to work even on .zip files, which is weird, but that is the cause of this regression.

Possible appropriate fixes:

• change 'untar' to 'unpack' and let it always use file extension
• add if-else to call 'unzip' or 'untar' depending on file extension

The second may be better and is definitely less risky, only use 'unzip' if the file ends with '.zip', always fall back to 'untar' to work the way the function used to. It also consistently uses Matlab compatible functions 'untar' and 'unzip', 'unpack' is Octave specific.

Originally reported at https://lists.gnu.org/archive/html/octave-maintainers/2019-02/msg00198.html.