treewide changes to convert incorrect usages of string.Length() to string.IsEmpty(). thanks to afatecha@idea.com.py (Ariel Fatecha) for the patch. r=dwitte, sr=jst. got the ok from Asa to land into a closed tree. git-svn-id: svn://10.0.0.236/trunk@142828 18797224-902f-48f8-a5cc-f745e15eee43