changed some of the "A"s in the UNPACK constant to "a"

... to allow trailing whitespaces in an archived filename

As of 2.02, Archive::Tar doesn't correctly extract an archive like NEILB/BackPAN-Index-Create-0.12.tar.gz which contains "t/testpan/authors/id/P/PO/POGLE/Wood-Pogle-0.001.tar.gz" and "t/testpan/authors/id/P/PO/POGLE/Wood-Pogle-0.001.tar.gz " (with a trailing whitespace, which is ignored). Changing some of the "A"s in the UNPACK constant should fix this.