If a state gets reset and you still hold a pointer to the previous,
incorrect, state object you'll operate on the wrong object. Using the
state to set/get objects and attributes you won't have this problem
since the state will always have the correct object.

* CALLVALUE pushed incorrect value to the stack
* Set execution model to closure

Standard VM should be about 10x faster than the debug VM. Some error
checking has been removed, all of the log statements and therefor quite
some unnecessary if-statements.

Fix filter map race

Fix Eventer race

This commit also documents (but doesn't enforce) that filters
are immutable while they're installed. This required a minor API
change.

This test reports the race condition when run
using "go test -race".