Clear too agressive on MacOS

[dsandstrom]

I saw that the clear command was changed by 5f4ab94 .

The problem this causes is that this removes past test results. I don't always have my eye on the results. And after multiple test iterations are run, there is no way to scroll up to see if the previous tests passed or not.

For example, I will hit enter to run all test. Then continue working on a file, then save it. Guard will then run the file's tests after running all tests. If errors pop up from "all tests" there will no way for me to see them because the file's tests just cleared the console.

I propose going back to just plain clear or adding another option. I will disable clearing for now.

[dsandstrom]

Link #858