Type checker correction for "while true" loops

[joey-coleman]

The following bug was originally reported on Sourceforge by nick_battle, 2013-11-20 07:48:20.119000:

The type checker had a fault where infinite while loops were not treated as such. For example, the following operation:

op: set of Event ==> Event
op(events) ==
    while true do
        for all e in set events do
            if e.isSignalled()
            then return e;

This raised an error, saying the operation returns "() | Event", since the loop was considered to terminate. The fix looks explicitly for "while true" loops like this, and so this now returns just "Event", as the signature requires.

[nickbattle]

Changes migrated into ncb/development.