Add JRCS sources to xwiki-external maven repository

Since the JRCS library project is almost dead and it was very difficult to found the sources, I suggest (and Vincent agree) that these has to be added into the xwiki-external maven repository for safety.

I have found them here:

http://download.java.net/maven/2/org/jvnet/hudson/org.suigeneris.jrcs.rcs/0.4.2/org.suigeneris.jrcs.rcs-0.4.2-sources.jar
http://download.java.net/maven/2/org/jvnet/hudson/org.suigeneris.jrcs.diff/0.4.2/org.suigeneris.jrcs.diff-0.4.2-sources.jar

I also attach them to this issue.