stringutil: teach pprint() to indent This will make data structure dumping in various places a bit easier to read and diff. Since I wanted this for `hg debugwireproto` output, I added indentation to it. A more advanced pretty printer implementation would conditionally add newlines if output is too long. But it is vastly simpler to be consistent and always add newlines when indenting. Again, I'm not crazy about the verbosity of the code and there is room to consolidate logic for "print a collection." But this isn't the most complicated code in the world and I'm not convinced it is worth doing. Differential Revision: https://phab.mercurial-scm.org/D4399

  $ hg init
  $ echo This is file a1 > a
  $ hg add a
  $ hg commit -m "commit #0"
  $ echo This is file b1 > b
  $ hg add b
  $ hg commit -m "commit #1"
  $ hg update 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo This is file c1 > c
  $ hg add c
  $ hg commit -m "commit #2"
  created new head
  $ hg merge 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ rm b
  $ echo This is file c22 > c

Test hg behaves when committing with a missing file added by a merge

  $ hg commit -m "commit #3"
  abort: cannot commit merge with missing files
  [255]