notify: fix fromauthor setting for 'incoming' hook type (issue4194)

Set the author field in notification emails for the 'incoming' hook type
in addition to 'changegroup' and 'outgoing' types.

hgext/notify.py

@@ -406,6 +406,8 b' def hook(ui, repo, hooktype, node=None, '
             return
         count += 1
         n.diff(ctx)
+        if not author:
+            author = ctx.user()
 
     data += ui.popbuffer()
     fromauthor = ui.config('notify', 'fromauthor')