Fix INT_MIN trade exploit (Fixes #2096)
Fix button graphics preventing mouse clicks (Fixes #2104)
Make MODL subrecord for light records optional (Fixes #2114)
Added proper slow fall effect mechanics.
updated credits file
Merge branch 'master' of https://github.com/OpenMW/openmw
Fix for issue #2051.  Not perfect (can get into a lock in some situations) but usable.