Fix bug where Command.globs didn't delete the destination directory.
There was often a mix between absolute and relative paths and in the
previous version, the destination argument was usually an absolute
path where the glob array (from Dir['*']) was a relative path.
Using a test_dir helper method for tests.
Rudimentary tests for Jekyll::Command
Added directory_with_contents() to DRY up test code and ensure folders exist in TestCommand.
Using 1.8.7-compliant File.expand_path instead of >1.9 File.realpath
Merge pull request #862 from mojombo/fix-autogen-dest-prob

Stop DirectoryWatcher from watching the destination directory