Comment 4 for bug 998492

This should have been caught by previous work, but wasn't due to:

May 12 16:49:13 ubuntu plugininstall.py: Failed to find package object for /target/var/cache/apt/archives/libreoffice-core_1%3a3.5.3-0ubuntu1_i386.deb: "The cache has no package named 'libreoffice-core:i386'"