Deprioritize imports within a if TYPE_CHECKING: when processing import cycles

[JukkaL]

If an import is ignored at runtime (due to being in an if TYPE_CHECKING: or if MYPY: block), it should always be considered to be of the lowest priority when sorting import cycles. This is important, in particular, since the imports could well be of form from m import ..., which are given the highest priority right now.

There is more discussion in #481.

[gvanrossum]

I tried this (#2167) and it didn't work very well. We may try again in the future but for now I think it's a dead end, so I'm closing this.

[gvanrossum]

Sorry, reopening, we need both this and the cross-module deferred processing of functions I proposed in #481 (comment).

[gvanrossum]

Fixed by #2167.