The new ReadStringFromMemory() API does not work correctly with NSStrings that...

The new ReadStringFromMemory() API does not work correctly with NSStrings that have an explicit length and no NULL terminator
This checkin reverts NSString to the old behavior when appropriate, and cleans up the syntax to call the UTF Reader&Dumper function
Incidentally, add a "-d" command-line flag to redo.py with the same semantics as "-d" in dotest.py

llvm-svn: 180141