tests/test-hgk.t

hidden: move hiddenrevs set on the repository

This set is always accessed through the repo for now. Having this set
carried by the changelog make it complicated to:

- initialize it, computing hidden set may involve revset call
- lazy compute it, (1) only the changelog can detect someone access it,
                   (2) only the repo have enought knowledge to compute it.

In later version I expect he changelog to apply filtering itself and the set to
be carried by changelog again.

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
  committer test 0 0
  revision 0
  branch default
  
  adda

  $ cd ..