While loading overwrite records with the same id.  Should resolve bug #1750.
Re-check unknown record id after loading.
Revert old fix.
Add 'const' to a spell helper function.
fixed resources table drag source problem
Disease check:  Reuse corprus check from spells.hpp.
Disease Check:  Shorten the resistance calculations.
Merge remote-tracking branch 'cc9cii/Bug-No-1750'
Merge remote-tracking branch 'scrawl/master'
Merge remote-tracking branch 'jordan-ayers/topic/disease-cleanup'
Merge branch 'master' of https://github.com/OpenMW/openmw
Fix journal quest logs not being marked finished when there are multiple quest IDs in the log