tarlz --diff broken

[Devon Sean McCullough]

tarlz --create and tarlz --diff fail to work compatibly.
The present incompatible --diff gets spurious errors.

                Peace
                        --Devon

P.S.  Existing scripts which depend on the present broken behavior,
applying the last --directory option to preceding files and looking
for them in the wrong place, ignoring the default directory and all
but the last --directory option, should get a warning, maybe even a
TARLZ_DIFF_INCOMPATIBLE environment variable to retain the old bug.

$ tarlz --create --directory=/dir/a foo --directory=/dir/b bar >bug.tlz
$ tarlz --diff --directory=/dir/a foo --directory=/dir/b bar <bug.tlz
tarlz: foo: warning: Can't stat: No such file or directory
$ ls -lR
.:
total 12
drwxr-xr-x 2 devon devon 4096 Sep  1 12:29 a
drwxr-xr-x 2 devon devon 4096 Sep  1 12:29 b
-rw-r--r-- 1 devon devon  172 Sep  1 12:59 bug.tlz

./a:
total 4
-rw-r--r-- 1 devon devon 4 Sep  1 12:29 foo

./b:
total 4
-rw-r--r-- 1 devon devon 4 Sep  1 12:29 bar

## Argument parsing should warn and shine a ray of hope, e.g.,
tarlz: --diff --directory semantics may change in the future.
## whenever a --directory option follows a file name.

## Also, the first "no such" message should be augmented, e.g.,
tarlz: in directory /dir/b
tarlz: foo: warning: can't stat: no such file or directory
## to clarify the bogus error.