later at pkg_delete time to verify that you're deleting what you added.
This, of course, does NOT cover the case where a file you still need
hasn't changed! That's a tougher problem to solve, and this provides
only the minimal amount of safety belt. MD5 checksums are stored in comment
fields, so packages produced with these tools are backwards compatible with
the older ones.
in the packing list, or the argument to -p if it is specified, before
the requirements/installation/deinstallation scripts are called. This
enables the scripts to be written to work on the final installation
destination, even if the user uses -p to override the package's default.
