upgrade issue: trying to overwrite '/usr/bin/swig', which is also in package swig 2.0.11-1ubuntu2

[Adam Gandelman]

in the process of dist-upgrad'ing from trusty -> xenial, hit this :

Preparing to unpack .../swig2.0_2.0.12-1ubuntu4_amd64.deb ...
Unpacking swig2.0 (2.0.12-1ubuntu4) over (2.0.11-1ubuntu2) ...
dpkg: error processing archive /var/cache/apt/archives/swig2.0_2.0.12-1ubuntu4_amd64.deb (--unpack):
 trying to overwrite '/usr/bin/swig', which is also in package swig 2.0.11-1ubuntu2
Preparing to unpack .../syslinux_3%3a6.03+dfsg-11ubuntu1_amd64.deb ...
Unpacking syslinux (3:6.03+dfsg-11ubuntu1) over (3:4.05+dfsg-6+deb8u1) ...
Preparing to unpack .../syslinux-common_3%3a6.03+dfsg-11ubuntu1_all.deb ..

ending in:

Processing triggers for ccache (3.2.4-1) ...
Updating symlinks in /usr/lib/ccache ...
Processing triggers for python-support (1.0.15) ...
Errors were encountered while processing:
 /var/cache/apt/archives/swig2.0_2.0.12-1ubuntu4_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)