Bug#1750: tar doesn't handle default remote arguments

[Bdale Garbee <bdale@gag.com>]

Package: tar
Version: 1.11.8

When attemping to do remote tar operations using the archive name systax
specified in the info file, which is "user@host:file", if user is not
specified, tar core dumps, when it should use the current username as the
default.

This is probably part of the same problem that resulted in bug report
#1110, but the problem is sufficiently different from what was reported
before that I decided to elaborate.  Feel free to attach this to bug #1110
if that seems appropriate.

You can duplicate this by doing

	tar tvf winfree:/dev/nrst0

when logged into hipshack as 'bdale', which will generation a segmentation
violation core dump, while using

	tar tvf bdale@winfree:/dev/nrst0

works fine.  Blech.