To import SQL files `connect` has to be used instead of `import`. Doing
so can’t work with the `-t` docker option, so now we check for a tty
before using this option.
Fixes#18
- dokku 0.4.0 does not yet exist, so this should dissuade people from installing this plugin.
- docker 1.8.x cannot be installed with the official dokku debian packages, so this means that for now users will need to install from source.