Merge: Nitin catches the runtime errors

~~~
-->abort
1,1--5: Runtime error: Aborted
	abort
	^
,---- Stack trace -- - -  -
| input-1$Sys$main (1,1--5)
`------------------- - -  -
-->fun toto is abstract
-->toto
1,1--20: Runtime error: Abstract method `toto` called on `Sys`
	fun toto is abstract
	^
,---- Stack trace -- - -  -
| input-2$Sys$toto (1,1--20)
| input-3$Sys$main (1,1--4)
`------------------- - -  -
-->class A
...var a: String is noautoinit
...fun foo do print a
...end
-->(new A).foo
3,18: Runtime error: Uninitialized attribute _a
	fun foo do print a
	                 ^
,---- Stack trace -- - -  -
| input-4$A$foo (3,18)
| input-5$Sys$main (1,1--11)
`------------------- - -  -
-->
~~~

Pull-Request: #2413