Änderungen

new compilation error when trying to access destroyed var
as suggested by Frotty in #731
when a local variable or 'this' has been destroyed this is stored in the 
control flow analysis and subsequent uses of the variable become an 
error. Note that this is not a complete analysis, it will not detect 
aliasing problems and does not do inter-procedure analysis, for example:
let a = new A() let b = a destroy b a.doSomething() // just a runtime
error
 (commit: 41868a9)