PDFBOX-2236: replace bouncycastle clone method with copyof, as suggested by Cyril Bremaud

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/branches/1.8@1612855 13f79535-47bb-0310-9956-ffa450edef68
PDFBOX-2236: use method supported in JDK5

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/branches/1.8@1612868 13f79535-47bb-0310-9956-ffa450edef68