[hacknews] improved error messages from tape

hat@utzoo.UUCP (Heather Trueman) (04/05/84)

Tape(1) has been updated to use openable(1) to test if tape device can
be opened for reading (and for writing when create or add options specified)
and to provide tailored messages if the test fails or if tar(1) returns
a non-zero exit status.