mtest 0.8.5

• An output cut at its limit says so (#22). e2e::run keeps at most 1 MiB
  of a program's standard error (256 MiB of its standard output), and an outcome cut there looked
  complete: a case that searched it could not tell an absent line from a dropped one. The outcome
  now carries out_truncated, err_truncated and held_open as mcpplibs.os reports them; a
  command states its own limits (out_limit, err_limit, the former values by default); and a
  failed succeeded or exited names the output that was cut and its size. Nothing changes for an
  output within its limit.
• CI caches the package store with its ABI directory. The store alone, restored, held the emsdk
  compiler without the loader its interpreter names, and the Web row of 0.8.4's release failed with
  "provides no std module source"; a store cached before this is not restored.