libappindicator3 not multilib aware, amd64 and i386 versions conflict

[Tim Brown]

Trying to install the amd64 and i386 versions of libappindicator3 on trusty, xenial and artful all fail with a message similar to the following:

tim@ubuntu-artful:~$ sudo apt install libappindicator3-1 libappindicator3-1:i386
Reading package lists... Done
Building dependency tree
Reading state information... Done
libappindicator3-1 is already the newest version (12.10.1+17.04.20170215-0ubuntu2).
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
 libappindicator3-1 : Conflicts: libappindicator3-1:i386 but 12.10.1+17.04.20170215-0ubuntu2 is to be installed
 libappindicator3-1:i386 : Depends: libindicator3-7:i386 (>= 0.4.90) but it is not going to be installed
                           Conflicts: libappindicator3-1 but 12.10.1+17.04.20170215-0ubuntu2 is to be installed
E: Unable to correct problems, you have held broken packages.