tests/test-debugindexdot.t

progress: use 'encoding.colwidth' to get column width of output line correctly

Before this patch, 'progress' extension applies 'len' on byte sequence
to get column width of it, but it causes incorrect result, when length
of byte sequence and columns in display are different from each other
in multi-byte characters.

This patch uses 'encoding.colwidth' to get column width of output line
correctly, even if it contains multi-byte characters.

Just exercise debugindexdot
Create a short file history including a merge.
  $ hg init t
  $ cd t
  $ echo a > a
  $ hg ci -qAm t1 -d '0 0'
  $ echo a >> a
  $ hg ci -m t2 -d '1 0'
  $ hg up -qC 0
  $ echo b >> a
  $ hg ci -m t3 -d '2 0'
  created new head
  $ HGMERGE=true hg merge -q
  $ hg ci -m merge -d '3 0'

  $ hg debugindexdot .hg/store/data/a.i
  digraph G {
  	-1 -> 0
  	0 -> 1
  	0 -> 2
  	2 -> 3
  	1 -> 3
  }

  $ cd ..