Merge branch 'master' into t

* master: (27 commits)
  setup: Fix hooking of git_lsfiles in PEP517 mode
  lib/zodb: Add zstor_2zurl - way to convert a ZODB storage into URL to access it
  lib/zodb: Add patch to ZODB.Connection to support callback on connection DB view change
  lib/zodb: Add zconn_at draft (ZODB5 only)
  lib/zodb: Add zmajor - way to know under which ZODB 3, 4 or 5 we are running
  bigfile/zodb: Cosmetics
  bigfile/file.h: Cosmetics
  bigfile/virtmem: vma_page_addr: Kill wrong XXX
  bigfile/virtmem: Factor-out checking whether `page->fpgoffset` is in file-range covered by `vma`
  bigfile/virtmem: fileh_mmap: Refactor a bit
  bigfile/virtmem: vma_mmap_page: Don't skip mmap_page error silently
  bigfile/virtmem: Factor-out mmaping Page into VMA into vma_mmap_page
  bigfile/virtmem: page_del: Assert that Page is not on fileh->dirty list
  bigfile/virtmem: Factor-out Page struct freeing into page_del
  bigfile/zodb: Factor-out patch for ZODB.Connection.onOpenCallback into -> lib/zodb
  *: Kill unused imports
  bigfile/py: Move data structures to public .h file
  bigfile/py: Provide package-level documentation
  bigfile/py: Stop using Plan9 C extensions
  bigfile/zodb: Factor-out LivePersistent into -> lib/zodb
  ...