Always interrupt page faulters on PageCache.close

Fixes a bug where threads stuck in grabFreePage, blocked waiting for new pages
to be freed, could get stuck there if the page cache was concurrently closed
_and_ the eviction thread was in the middle of evicting pages.
Merge pull request #3328 from chrisvest/2.2-pc-shutdown-fault-race

Always interrupt page faulters on PageCache.close