When freeing a cert_list_t, avoid memory leak.

We were freeing these on exit, but when we added the dl_status_map
field to them in fddb814f, we forgot to arrange for it to be freed.

I've moved the cert_list_free() code into its own function, and added
an appropriate dsmap_free() call.

Fixes bug 9644; bugfix on 0.2.4.13-alpha.
Merge branch 'bug9644_024' into maint-0.2.4