Use bsdtar(1) for unpacking ZIP format files.

     Change: use-bsdtar-for-zip-files
     Purpose: Use bsdtar(1) for unpacking ZIP format files.
     Reason: OpenPKG uses bsdtar(1) to unpack ZIP format files to
                     avoid having to bundle the less portable unzip(1)
                     into the bootstrap package.
     Hint: If RPM would use "%__unzip -qq" instead of "%{__unzip} -qq"
                     one could also use plain macros in OpenPKG to
                     convert the call to unzip(1) to bsdtar(1). But I
                     don't wanted to change RPM here as all other macros
                     are also just for the expansion of the command and
                     not for the complete command argument line.