removes duplicated method from Rakefile
Merge pull request #102 from square/rudle/remove-doubly-defined-method

removes duplicated method from Rakefile
Cleanup bad merge from #72.

* Run the 'brew tap' command rather than just creating a string.
* Fail if the 'brew tap' command fails.
* Run ruby code in ruby, not by shelling out to the system! oO
Merge pull request #104 from square/donovan/cleanup-after-72

Cleanup bad merge from #72.
check for presence of cask before installing it
Merge pull request #105 from square/rudle/safer-brew-tap

check for presence of cask before installing it
fixup abort message