Fix test-notify for systems without or with a different version of diffstat.

Some diffstat versions say "1 file changed", others "1 files changed".

tests/test-notify

@@ -1,38 +1,39 b''
 #!/bin/sh
 
 cat <<EOF >> $HGRCPATH
 [extensions]
 notify=
 
 [hooks]
 incoming.notify = python:hgext.notify.hook
 
 [notify]
 config = $HGTMP/.notify.conf
 sources = pull
 domain = test.com
 strip = 3
 template = Subject: {desc|firstline|strip}\nFrom: {author}\n\nchangeset {node|short} in {webroot}\ndescription:\n\t{desc|tabindent|strip}
+diffstat = False
 
 [web]
 baseurl = http://test/
 
 [usersubs]
 foo@bar = *
 EOF
 
 hg init a
 echo a > a/a
 echo % commit
 hg --traceback --cwd a commit -Ama -d '0 0'
 
 echo % clone
 hg --traceback clone a b
 
 echo a >> a/a
 echo % commit
 hg --traceback --cwd a commit -Amb -d '1 0'
 
 echo % pull
 hg --traceback --cwd b pull ../a 2>&1 | sed -e 's/\(Message-Id:\).*/\1/' \
   -e 's/changeset \([0-9a-f]*\) in .*/changeset \1/'

tests/test-notify.out

@@ -1,35 +1,30 b''
 % commit
 adding a
 % clone
 1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 % commit
 % pull
 pulling from ../a
 searching for changes
 adding changesets
 adding manifests
 adding file changes
 added 1 changesets with 1 changes to 1 files
 Subject: b
 From: [e-mail]
 X-Hg-Notification: changeset 0647d048b600
 Message-Id:
 To: foo@bar
 
 changeset 0647d048b600
 description:
 	b
-diffstat:
-
-1 file changed, 1 insertion(+)
-a |    1 +
-
 diffs (6 lines):
 
 diff -r cb9a9f314b8b -r 0647d048b600 a
 --- a/a	Thu Jan 01 00:00:00 1970 +0000
 +++ b/a	Thu Jan 01 00:00:01 1970 +0000
 @@ -1,1 +1,2 @@ a
  a
 +a
 (run 'hg update' to get a working copy)