Add exclusion for OSX ._<filename> files

Exclude older OSX metadata ._<filename> files from sync, improving
cross-platform sync experience.

Tested-on: arcturus <20 Nov 2013>

sync-exclude.lst

@@ -13,6 +13,7 @@ csync_journal.db.ctmp
 
 ].DS_Store
 ].ds_store
+._*
 ]Thumbs.db
 desktop.ini