Make CoreRunnable lock mutable
Make CoreRunnable lock mutable

This lock should be usable in `const` accessor methods without requiring any special casting.  Locks, generally speaking, ought to be mutable because they may sometimes need to synchronize access to data that may be read-only in the current context.

codemercenary/autowiring,leapmotion/autowiring,leapmotion/autowiring,codemercenary/autowiring,leapmotion/autowiring,leapmotion/autowiring,codemercenary/autowiring,codemercenary/autowiring,leapmotion/autowiring,codemercenary/autowiring,codemercenary/autowiring,leapmotion/autowiring