COMP: Fix configuration adding missing parameter to ExternalProject_Add_Source

Following commit r22776, the macro ExternalProject_Add_Source has been
added and jqPlot retrieved using it but the URL and URL_MD5 parameters
were not considered. This probably happens because the jqPlot directory
was already existing.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22781 3bd1e089-480b-0410-8dfb-8563597acbee