Athletics skill increase

Note the bug in getSkillGain. There was a missing brace: http://wiki.openmw.org/index.php?title=Research:Stats_and_Levelling#Skill_increases
The bug was causing higher skill use values to produce less skill gain, and the other way round.

http://forum.openmw.org/viewtopic.php?f=2&t=1381&p=15942#p15942

Athletics increase seems mostly accurate but the level times don't match exactly.
This seems to be due to a funny bug in vanilla: The skill is actually increased before the progress is at 100% (from my tests at about 89%). This behaviour isn't really worth replicating.