Trying to delete a plugin that has been used by a job results in foreign key exception

[Nicklas Nordborg]

Pb on the trashcan when attempting to remove a plugin definition and associated jobs have not been removed.

here is the error message

Operating system     Windows XP x86 5.1
Memory     Total: 127.1 MB
Free: 90.0 MB
Max: 508.1 MB
Browser     Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.9) Gecko/20071025 Firefox/2.0.0.9
Error message     Cannot delete or update a parent row: a foreign key constraint fails (`base2/jobs`, CONSTRAINT `FK23507617401FCE` FOREIGN KEY (`plugindefinition_id`) REFERENCES `plugindefinitions` (`id`))
Stack trace    

DatabaseException
...at HibernateUtil.commit(HibernateUtil.java:918)
...at DbControl.commit(DbControl.java:393)
...at Trashcan.delete(Trashcan.java:230)
...at org.apache.jsp.views.trashcan.index_jsp._jspService(index_jsp.java:269)
...at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
...at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
...at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
...at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)

[Nicklas Nordborg]

(In [3949]) Fixes #820