tests/test-absorb-edit-lines.t

verify: allow the storage to signal when renames can be tested on `skipread`

This applies the new marker in the lfs handler to show it in action, and adds
the test mentioned at the beginning of the series to show that fulltext isn't
necessary in the LFS case.

The existing `skipread` isn't enough, because it is also set if an error occurs
reading the revlog data, or the data is censored.  It could probably be cleared,
but then it technically violates the interface contract.  That wouldn't matter
for the existing verify algorithm, but it isn't clear how that will change as
alternate storage support is added.

The flag is probably pretty revlog specific, given the comments in verify.py.
But there's already filelog specific stuff in there and I'm not sure what future
storage will bring, so I don't want to over-engineer this.  Likewise, I'm not
sure that we want the verify method for each storage type to completely drive
the bus when it comes to detecting renames, so I don't want to go down the
rabbithole of having verifyintegrity() return metadata hints at this point.

Differential Revision: https://phab.mercurial-scm.org/D7713

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > absorb=
  > EOF

  $ hg init repo1
  $ cd repo1

Make some commits:

  $ for i in 1 2 3; do
  >   echo $i >> a
  >   hg commit -A a -m "commit $i" -q
  > done

absorb --edit-lines will run the editor if filename is provided:

  $ hg absorb --edit-lines --apply-changes
  nothing applied
  [1]
  $ HGEDITOR=cat hg absorb --edit-lines --apply-changes a
  HG: editing a
  HG: "y" means the line to the right exists in the changeset to the top
  HG:
  HG: /---- 4ec16f85269a commit 1
  HG: |/--- 5c5f95224a50 commit 2
  HG: ||/-- 43f0a75bede7 commit 3
  HG: |||
      yyy : 1
       yy : 2
        y : 3
  nothing applied
  [1]

Edit the file using --edit-lines:

  $ cat > editortext << EOF
  >       y : a
  >      yy :  b
  >      y  : c
  >     yy  : d  
  >     y y : e
  >     y   : f
  >     yyy : g
  > EOF
  $ HGEDITOR='cat editortext >' hg absorb -q --edit-lines --apply-changes a
  $ hg cat -r 0 a
  d  
  e
  f
  g
  $ hg cat -r 1 a
   b
  c
  d  
  g
  $ hg cat -r 2 a
  a
   b
  e
  g