Switch cm::ValueOfPointer dereferencing to int.

This is in preparation for supporting negative dereferences (we'll need
to add a new method to retrieve the lowest valid dereference, and update
the existing clients to use it).
Don't set thread time when readding several event types.

Also, when adding event types, assert that the thread time is always
incremented. This indicates that we should be able to remove the
thread time field from many events.
Remove unused method EventRecordBase::getThreadTime().
Don't use thread time field from events.

Simply increment/decrement the current thread time as appropriate.
Remove the ThreadTime property from most events.

This is no longer used. Removing it results in a substantial reduction
in the size of most execution traces.