Try/finally not counted as definite assignment

[floitsch]

The following program yields an error:

class A:
  foo/int

  constructor:
    try:
      foo = 499
    finally:
      print "done"

ᐅ toit analyze /tmp/t.toit
/tmp/t.toit:4:3: error: Field 'foo' not initialized on all paths in constructor
  constructor:
  ^~~~~~~~~~~