0.13.6 eviction notices too noisy

It's pretty cool that SBT now lets me know of evictions. The problem with it is that it warns so often; I think we need a way to say _I'm aware of eviction X, please don't bug me about it_.

Example, this is what `~compile` looks like now for me.
```
[warn] There may be incompatibilities among your library dependencies.
[warn] Here are some of the libraries that were evicted:
[warn] 	* com.github.japgolly.fork.scalaz:scalaz-effect_sjs0.5_2.11:7.1.0-2 -> 7.1.0-3
[warn] Run 'evicted' to see detailed eviction warnings
[success] Total time: 0 s, completed 24/09/2014 5:18:43 PM
1. Waiting for source changes... (press enter to interrupt)
[warn] There may be incompatibilities among your library dependencies.
[warn] Here are some of the libraries that were evicted:
[warn] 	* com.github.japgolly.fork.scalaz:scalaz-effect_sjs0.5_2.11:7.1.0-2 -> 7.1.0-3
[warn] Run 'evicted' to see detailed eviction warnings
[success] Total time: 0 s, completed 24/09/2014 5:19:01 PM
2. Waiting for source changes... (press enter to interrupt)
[warn] There may be incompatibilities among your library dependencies.
[warn] Here are some of the libraries that were evicted:
[warn] 	* com.github.japgolly.fork.scalaz:scalaz-effect_sjs0.5_2.11:7.1.0-2 -> 7.1.0-3
[warn] Run 'evicted' to see detailed eviction warnings
[success] Total time: 0 s, completed 24/09/2014 5:19:04 PM
3. Waiting for source changes... (press enter to interrupt)
[warn] There may be incompatibilities among your library dependencies.
[warn] Here are some of the libraries that were evicted:
[warn] 	* com.github.japgolly.fork.scalaz:scalaz-effect_sjs0.5_2.11:7.1.0-2 -> 7.1.0-3
[warn] Run 'evicted' to see detailed eviction warnings
[success] Total time: 0 s, completed 24/09/2014 5:19:06 PM
4. Waiting for source changes... (press enter to interrupt)
[warn] There may be incompatibilities among your library dependencies.
[warn] Here are some of the libraries that were evicted:
[warn] 	* com.github.japgolly.fork.scalaz:scalaz-effect_sjs0.5_2.11:7.1.0-2 -> 7.1.0-3
[warn] Run 'evicted' to see detailed eviction warnings
[success] Total time: 0 s, completed 24/09/2014 5:19:08 PM
5. Waiting for source changes... (press enter to interrupt)
[warn] There may be incompatibilities among your library dependencies.
[warn] Here are some of the libraries that were evicted:
[warn] 	* com.github.japgolly.fork.scalaz:scalaz-effect_sjs0.5_2.11:7.1.0-2 -> 7.1.0-3
[warn] Run 'evicted' to see detailed eviction warnings
[success] Total time: 0 s, completed 24/09/2014 5:19:10 PM
6. Waiting for source changes... (press enter to interrupt)
[warn] There may be incompatibilities among your library dependencies.
[warn] Here are some of the libraries that were evicted:
[warn] 	* com.github.japgolly.fork.scalaz:scalaz-effect_sjs0.5_2.11:7.1.0-2 -> 7.1.0-3
[warn] Run 'evicted' to see detailed eviction warnings
[success] Total time: 0 s, completed 24/09/2014 5:19:13 PM
7. Waiting for source changes... (press enter to interrupt)
```