Fix listing of held packages in dpkg

Paul Wise reported the bug in Debian [1] along with a fix.  I forwarded
the fix upstream [2].  While a new version of bash-completion is not
provided, Debian carries the fix.

Thanks to Paul Wise for reporting and providing a fix.

[1] https://bugs.debian.org/907294

[2] https://github.com/scop/bash-completion/pull/250