Added some internal capability that allows to find out whether we're in the long living process (long living daemon). It is needed for the in-memory task artifacts cache.
Reduced log level INFO->DEBUG in one place.
Initial implementation of the in-memory task history cache.

1. The cache speeds up incremental daemon builds (~20%), at some expense of memory. The gc performance looks actually slightly better with this change.
2. The cache is capped (educated guess) so that smaller-to-big builds should take advantage of it. However, for huge builds we're not keeping *entire* task history cache in memory otherwise the performance is actually reduced (both: speed & memory).
3. Needs to be reworked in few places. I'm looking for a review!