Zonefile loading fixes

Most is said in the commit. I would have refactored zone-load more (especially the custom rrset lists could be standard ptrnode_t list from list.h) and a few other things, also it should be named something like zonefile.h as we already have a zone-load.h file which is for zone loading in general and makes it confusing. But I didnt, as @jkadlec made a lot of changes in the rrset->rrsigs and I suspect this would result in nasty collisions (like the rrset lists code). So... this should be done after his branch is merge-able.