Use java-processing to run sketches.

From Processing 2.0 beta 5, the 'use external editor' option has been removed. Instead, a processing-java command is supplied to run sketches from the command line. This commit updates vim-processing to allow use of processing-java.

To preserve backwards compatibility on OS X, the previous AppleScript utility will be used to run sketches by default. This behaviour can be overridden by setting g:use_processing_java=1. processing-java will be used by default on other platforms.