Merged apt-dependency-error-message [r=jseutter,tealeg] [f=921712].
Provide a better error message if AptFacade can't install some packages
due to dependencies not being satisfied.
The error message is made to look what apt-get or aptitude produces.
It's not quite the same, but it should be good enough.
One thing that it doesn't handle is Conflicts and Breaks dependency. I
discovered that late into the branch, and thought it would be better to
address that in another branch, so this can be landed.