Merge change I42d17725 into eclair-mr2

* changes:
  Cache NumberFormat and DecimalFormatSymbols objects in a ThreadLocal, so they can be reused between multiple instances of Formatter on the same thread.  This speeds up my unscientific benchmark (a number of printouts involved in a debugging diagnostics output) by 3x, and should have a similar impact on anyone who uses String.format(), PrintWriter.format(), and the like.