extdiff: add --change option to display single changeset diff

This is the counterpart for extdiff of 9c6ae2e09e11.

hgext/extdiff.py

@@ -117,7 +117,19 b' def dodiff(ui, repo, diffcmd, diffopts, '
       another one and more than 1 file is changed
     - just invoke the diff for a single file in the working dir
     '''
-    node1, node2 = cmdutil.revpair(repo, opts['rev'])
+
+    revs = opts.get('rev')
+    change = opts.get('change')
+
+    if revs and change:
+        msg = _('cannot specify --rev and --change at the same time')
+        raise util.Abort(msg)
+    elif change:
+        node2 = repo.lookup(change)
+        node1 = repo[node2].parents()[0].node()
+    else:
+        node1, node2 = cmdutil.revpair(repo, revs)
+
     matcher = cmdutil.match(repo, pats, opts)
     modified, added, removed = repo.status(node1, node2, matcher)[:3]
     if not (modified or added or removed):
@@ -205,6 +217,7 b' cmdtable = {'
      [('p', 'program', '', _('comparison program to run')),
       ('o', 'option', [], _('pass option to comparison program')),
       ('r', 'rev', [], _('revision')),
+      ('c', 'change', '', _('change made by revision')),
      ] + commands.walkopts,
      _('hg extdiff [OPT]... [FILE]...')),
     }

tests/test-extdiff

@@ -32,9 +32,14 b' hg update 0'
 echo c >> c
 hg add c
 hg ci -m "new branch" -d '1 0'
-hg update -C 1
-hg merge tip
+hg merge 1
 # should diff cloned file against wc file
-hg falabala > out || echo "diff-like tools yield a non-zero exit code"
+hg falabala > out
 # cleanup the output since the wc is a tmp directory
 sed  's:\(.* \).*\(\/test-extdiff\):\1[tmp]\2:' out
+# test --change option
+hg ci -d '2 0' -mtest3
+hg falabala -c 1
+# check diff are made from the first parent
+hg falabala -c 3 || echo "diff-like tools yield a non-zero exit code"
+#hg log

tests/test-extdiff.out

@@ -20,6 +20,7 b' options:'
 
  -o --option   pass option to comparison program
  -r --rev      revision
+ -c --change   change made by revision
  -I --include  include names matching the given patterns
  -X --exclude  exclude names matching the given patterns
 
@@ -27,8 +28,9 b' use "hg -v help falabala" to show global'
 diffing a.8a5febb7f867/a a.34eed99112ab/a
 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 created new head
-1 files updated, 0 files merged, 1 files removed, 0 files unresolved
 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 (branch merge, don't forget to commit)
+diffing a.2a13a4d2da36/a [tmp]/test-extdiff/a/a
+diffing a.8a5febb7f867/a a.34eed99112ab/a
+diffing a.2a13a4d2da36/a a.46c0e4daeb72/a
 diff-like tools yield a non-zero exit code
-diffing a.34eed99112ab/c [tmp]/test-extdiff/a/c