Bump version to 0.9.3.1.99 for development

Author: wch

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: ggplot2
 Type: Package
 Title: An implementation of the Grammar of Graphics
-Version: 0.9.3.1
+Version: 0.9.3.1.99
 Author: Hadley Wickham <h.wickham@gmail.com>, Winston Chang <winston@stdout.org>
 Maintainer: Hadley Wickham <h.wickham@gmail.com>
 Description: An implementation of the grammar of graphics