Make POOL_FLAG_ADDFILEPROVIDESFILTERED behaviour more standard

Make POOL_FLAG_ADDFILEPROVIDESFILTERED behaviour more standard

Turning on POOL_FLAG_ADDFILEPROVIDESFILTERED made the lookup of
all file dependencies lazy, not only the ones required by some
dependency. This changes the way searching works and may also
slow down some use cases.

We now changed addfileprovides() to record the needed non-standard
file dependencies and only make those lazy in createwhatprovides().