pkgcachegen: Account for remapping when parsing depends from NewPackage

pkgcachegen: Account for remapping when parsing depends from NewPackage

In both the Ver and Dep variables, we need to account for remapping,
as otherwise we would still reference the old bug.

Reproduction environment:

* An i386 system with amd64 foreign architecture
* A sources.list with
deb http://snapshot.debian.org/archive/debian/20150826T102846Z/ unstable main
deb http://snapshot.debian.org/archive/debian/20150826T102846Z/ experimental main

Thanks: Jakub Wilk for the bug report and the backtraces
Closes: #796999