Bug#1000964: add way to run installation scripts with sh -x

[積丹尼 Dan Jacobson]

Package: dpkg
Version: 1.20.9
Severity: wishlist

Add a way to run /var/lib/dpkg/info/* scripts with sh -x instead of sh,
without needing to repackage a package just to put an set -x at the top
of a file.