Added support for an optional two-pass production for PostScript output to minimize...

Added support for an optional two-pass production for PostScript output to minimize file size. This adds images only once and adds only the fonts that are really used. The actual resource optimization is implemented with the use of the new DSC parser in XML Graphics Commons.
A simple test file with a few images and a few configured fonts of which most are not used shows, that with the two-pass approach the file size of the generated PostScript file decreased from 510KB to 160KB. Note that enabling this feature will increase the memory requirements in the PostScript interpreter when there are many images. Documentation follows.

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@513857 13f79535-47bb-0310-9956-ffa450edef68