properly recognize existing symlinks in linkapps

turns out a symlink of a directory is both a symlink and a directory, so
you have to test for symlink first if you want to catch it.

this should address #36

lib/cask.rb

@@ -129,13 +129,13 @@ class Cask
     destination_path.entries.select { |f| f.basename.to_s =~ /.app$/ }.each do |app|
       symlink_destination = HOME_APPS.join(app.basename)
       symlink_target = destination_path.join(app)
-      if symlink_destination.directory? || symlink_destination.file?
+      if symlink_destination.symlink?
-        puts "#{symlink_destination} already exists and is not a symlink, not linking #{self}"
-      elsif symlink_destination.symlink?
         puts "#{symlink_destination} exists but is symlink; removing and relinking"
         puts "#{symlink_destination} -> #{symlink_target}"
         symlink_destination.delete
         symlink_destination.make_symlink(symlink_target)
+      elsif symlink_destination.directory? || symlink_destination.file?
+        puts "#{symlink_destination} already exists and is not a symlink, not linking #{self}"
       else
         puts "#{symlink_destination} -> #{symlink_target}"
         symlink_destination.make_symlink(symlink_target)