When rendering to multiple image files, render to filename.NNNN.ext rather than filen...

When rendering to multiple image files, render to filename.NNNN.ext rather than filenameNNNN.ext.  When filename itself ends with a number, it's confusing to have the serial number merge with the filename.

git-svn-id: http://svn.voria.com/code@972 1f10aa63-cdf2-0310-b900-c93c546f37ac