Fixed Web UI build error caused by rhino changes in F19

rhino-1.7R4-2.fc19.noarch dropped -main flag which made the build fail in rawhide (F19).

We can't use the same command for rhino-1.7R3-6 (F18) and rhino-1.7R4-2 (F19).
This patch adds check if rhino supports '-require' option. If so it calls rhino with it if not it calls rhino with -main option.

https://fedorahosted.org/freeipa/ticket/3501