fix view-tar alias under MacOs

[tomasohara]

The view-tar alias is broken under MacOs:

$ view-tar akin.tar.gz | head -5
$


$ tar tvfz akin.tar.gz | head -5
drwxr-xr-x  0 jdoe  staff       0 Jun 22 00:05 akin/
-rw-r--r--  0 jdoe  staff      64 Jun 22 00:05 akin/__init__.py
drwxr-xr-x  0 jdoe  staff       0 Jun 22 00:05 akin/__pycache__/
-rw-r--r--  0 jdoe  staff    7700 Jun 22 00:05 akin/lsh.py
-rw-r--r--  0 jdoe  staff    7346 Jun 22 00:05 akin/minhash.py

The GTAR variable is causing problems:

$ cmd-trace view-tar akin.tar.gz | head
start: Mon Jul 15 19:55:24 CDT 2024
+ eval 'view-tar akin.tar.gz'
++ view-tar akin.tar.gz
++ gtar tvfz akin.tar.gz
++ less
++ gtar
++ gtar
++ gtar
++ gtar
++ gtar

$ GTAR=tar cmd-trace view-tar akin.tar.gz | head
start: Mon Jul 15 19:55:32 CDT 2024
+ eval 'view-tar akin.tar.gz'
++ view-tar akin.tar.gz
++ tar tvfz akin.tar.gz
++ less
drwxr-xr-x  0 jdoe  staff       0 Jun 22 00:05 akin/
-rw-r--r--  0 jdoe  staff      64 Jun 22 00:05 akin/__init__.py
drwxr-xr-x  0 jdoe  staff       0 Jun 22 00:05 akin/__pycache__/
-rw-r--r--  0 jdoe  staff    7700 Jun 22 00:05 akin/lsh.py
-rw-r--r--  0 jdoe  staff    7346 Jun 22 00:05 akin/minhash.py