[krbdev.mit.edu #6666] some non-default plugin directories don't build in 1.8 branch

[Ken Raeburn via RT]

Dependencies in plugins/kdb/hdb are out of date.  Actually, some others are too, but the hdb 
directory doesn't build.

Symbol export lists in plugins/preauth/cksum_body and plugins/preauth/wpse are out of date, 
and the code gets warnings from gcc about not being C90 compliant; pulling up r23736-
r23739 should fix both.