Ticket 407 - memory leak in dna plugin
Bug Description: Valgrind reported a memory leak in dna_pre_op()
Fix Description: Moved the slapi mod allocation, and freed the mods on error.
https://fedorahosted.org/389/ticket/407
Reviewed by: ?
(cherry picked from commit 9229db23f5491bf8320967387e88903334dfed94)