outline view info takes too long to refresh

[rhebus]

I currently have two perl documents open. If I ctrl-tab between them, it takes several seconds to recalculate the outline view -- even if it has been previously calculated. The outline view should be available instantly.

Either the algorithm should run so fast you don't notice it, or the information should be cached so that it isn't recalculated each time you switch tabs. (I think the cached solution is more likely feasible).

[Sewi]

Same issue as in #541, close both on fix.