[packagekit] Need a GetDependsFile function

[Richard Hughes]

According to https://bugzilla.redhat.com/show_bug.cgi?id=495523 we
need a GetDependsFile function so we can correctly list the deps of a
_file_ not a package so we can ask the user if they agree to deps.
Does anyone want to add the needed daemon code to make this happen? It
would be a good first job if you wanted to get familiar with the inner
workings of PackageKit, and I can review patches slowly and carefully
if needed. Thanks.

Richard.