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.

lib/jekyll/command.rb

@@ -3,7 +3,7 @@ module Jekyll
     def self.globs(source, destination)
       Dir.chdir(source) do
         dirs = Dir['*'].select { |x| File.directory?(x) }
-        dirs -= [destination]
+        dirs -= [destination, File.realpath(destination), File.basename(destination)]
         dirs = dirs.map { |x| "#{x}/**/*" }
         dirs += ['*']
       end