Wrap update_fsl_package

I think it makes sense for this binary to be easily available or is this considered a too advanced feature to expose like this?

post-link.sh

 if [ -e ${FSLDIR}/share/fsl/sbin/createFSLWrapper ]; then
-    ${FSLDIR}/share/fsl/sbin/createFSLWrapper fslversion update_fsl_release
+    ${FSLDIR}/share/fsl/sbin/createFSLWrapper fslversion update_fsl_release update_fsl_package
 fi