tests/test-merge-revert2.t

zsh_completion: declare appropriate local parameters for ->string form

When ->string form is used for _arguments, the function that calls it must
declare appropriate local parameters.

Managing local return value is needed to tell the completion system if our
function succeeded in suggesting something or not, plus without that `hg diff
-<TAB>` doesn't look right.

While at it, fix a copypaste error (s/diff_files/revert_files/).

Docs: http://zsh.sourceforge.net/Doc/Release/Completion-System.html

Differential Revision: https://phab.mercurial-scm.org/D4264

  $ hg init

  $ echo "added file1" > file1
  $ echo "another line of text" >> file1
  $ echo "added file2" > file2
  $ hg add file1 file2
  $ hg commit -m "added file1 and file2"

  $ echo "changed file1" >> file1
  $ hg commit -m "changed file1"

  $ hg -q log
  1:dfab7f3c2efb
  0:c3fa057dd86f
  $ hg id
  dfab7f3c2efb tip

  $ hg update -C 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg id
  c3fa057dd86f

  $ echo "changed file1" >> file1
  $ hg id
  c3fa057dd86f+

  $ hg revert --no-backup --all
  reverting file1
  $ hg diff
  $ hg status
  $ hg id
  c3fa057dd86f

  $ hg update
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg diff
  $ hg status
  $ hg id
  dfab7f3c2efb tip

  $ hg update -C 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo "changed file1 different" >> file1

  $ hg update
  merging file1
  warning: conflicts while merging file1! (edit, then use 'hg resolve --mark')
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges
  [1]

  $ hg diff --nodates
  diff -r dfab7f3c2efb file1
  --- a/file1
  +++ b/file1
  @@ -1,3 +1,7 @@
   added file1
   another line of text
  +<<<<<<< working copy: c3fa057dd86f - test: added file1 and file2
  +changed file1 different
  +=======
   changed file1
  +>>>>>>> destination:  dfab7f3c2efb - test: changed file1

  $ hg status
  M file1
  ? file1.orig
  $ hg id
  dfab7f3c2efb+ tip

  $ hg revert --no-backup --all
  reverting file1
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  dfab7f3c2efb tip

  $ hg revert -r tip --no-backup --all
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  dfab7f3c2efb tip

  $ hg update -C
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg diff
  $ hg status
  ? file1.orig
  $ hg id
  dfab7f3c2efb tip