Issue #42. Incorrect directory creation error with using boiler command

## fix error display when boiler commands tries to create app directory

couchapp boiler &lt;appname&gt; _or_
couchapp boiler .

In the first case, couchapp created the app directory in the #boiler function. In the second case, the user has already created the app directory.

Running the boiler command issued an error when trying to create the app directory. Despite the error the command still worked as expected, the error was just misleading to users, hence issue #42

#copytree was attempting to create the root app directory and displaying an error. This pull request adds a check  to prevent the creation of the app directory, thus removing the error output