tests/test-fastannotate-diffopts.t

diff: replace --merge option by config option

I can't think of any reason you'd want to enable the merge diff on a
run-to-run basis; you'd probably either always or never want it set
(though I can't see why you'd never want it set). If you have it set,
you'll probably also want the same output in `hg log -p`
output. Having a single config option for the feature makes sense.

Differential Revision: https://phab.mercurial-scm.org/D9956

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

  $ hg init repo
  $ cd repo

changes to whitespaces

  $ cat >> a << EOF
  > 1
  > 
  >  
  >  2
  > EOF
  $ hg commit -qAm '1'
  $ cat > a << EOF
  >  1
  > 
  > 2
  > 
  > 
  > 3
  > EOF
  $ hg commit -m 2
  $ hg fastannotate -wB a
  0:  1
  0: 
  1: 2
  0: 
  1: 
  1: 3