deploy incompatible charm using --to should error earlier

[Ian Booth]

Deploying a multi-series charm supporting say trusty and precise to a wily machine using the --to parameter:

$ juju deploy cs:mysql --to 1

The command runs ok, but then status shows an error for the unit:

cannot assign unit "mysql/0" to machine 1: series does not match

This is too late. The deploy command should exist with an error in the first place (unless --force is used).