The latter state is the only valid state in wcfs mode when pagefault
handler sees already loaded page in fileh->pagemap.

* master:
  bigfile: Note that ramh_alloc_page does not add the page to any lists
  bigfile: Unstub ram_close

It was already said there that allocated page is not associated with
fileh. However the code is doing more - it does not add the page to
ram->lru_list and (obviously) to fileh->dirty_pages lists.

Document that explicitly.

It should release resources associated with RAM. Make it call .ram_close
from RAM ops. Add corresponding .ram_close to ram_shmfs. This fixes
SHMFS_RAM->prefix leak.

* master:
  bigfile: Note that ramh_alloc_page does not add the page to any lists
  bigfile: Unstub ram_close
  bigfile/test/test_ram: Don't forget to free allocated Page structs
  bigfile: RAM must be explicitly free'ed after close
  bigfile/test: Don't forget to close opened RAM
  tests: TSAN no longer fails on test_virtmem
  tox: Don't duplicate setup.py on which for-tests dependencies we need
  3rdparty/ccan: Update