RFR 8189838: Stack overflow when computing upward projection of an intersection type with fbounds

[Maurizio Cimadamore]

Hi,
the patch fixes a bug in the logic for detecting fbounds loop in the 
LVTI upward projection logic. Basically when we recurse projection on a 
type-variable (upper) bound, we must keep track of the variable 
somewhere, as the bound can contain the variable itself, and lead to 
infinite loops.

I was aware of the situation and the original code was already doing 
something in this regard - however, the try/finally used to add/remove 
the variable to the list of seen variables was too broad, and it ended 
up also removing type-var in case of cycles, thus defeating the purpose 
of the logic, at least in certain examples.

I've rectified the logic so that now a variable is removed from the list 
at the end of its projection _only_ if no cycle has been detected. Also, 
when a cycle is indeed detected, we need to return either Object or 
<null> depending on the projection kind.

Webrev here:

http://cr.openjdk.java.net/~mcimadamore/8189838/

Cheers
Maurizio