tests/test-hgk.t

relink: abort earlier when on different devices (issue3916)

Add a first check of the devices before collecting candidate files. This is
much quicker when big repos are on different devices.
Keep the existing check in prune. It checks for same device of the files. This
could probably be different in a special repo store (with symlinks).

Minimal hgk check

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "hgk=" >> $HGRCPATH
  $ hg init repo
  $ cd repo
  $ echo a > a
  $ hg ci -Am adda
  adding a
  $ hg debug-cat-file commit 0
  tree a0c8bcbbb45c
  parent 000000000000
  author test 0 0
  revision 0
  branch default
  phase draft
  
  adda

  $ cd ..