test: Fix HTML rendering test

The test designed to exercise Emacs' rendering of HTML emails
containing images inadvertently assumed w3m was available under Emacs
23.  The real point of this test was to check that Emacs 24's shr
renderer didn't crash when given img tags, so use shr if it's
available, html2text otherwise (which is built in), and do only a
simple sanity check of the result.

test/emacs

@@ -788,13 +788,12 @@ counter=$(test_emacs \
 test_expect_equal "$counter" 2
 
 
-test_begin_subtest "Rendering HTML mail with images"
 add_message '[subject]="HTML mail with images"' \
     '[content-type]="multipart/related; boundary=abcd"' \
     '[body]="--abcd
 Content-Type: text/html
 
-<img src="cid:330@goomoji.gmail">
+<img src="cid:330@goomoji.gmail"> smiley
 
 --abcd
 Content-Type: image/gif
@@ -804,21 +803,15 @@ Content-ID: <330@goomoji.gmail>
 R0lGODlhDAAMAKIFAF5LAP/zxAAAANyuAP/gaP///wAAAAAAACH5BAEAAAUALAAAAAAMAAwAAAMl
 WLPcGjDKFYi9lxKBOaGcF35DhWHamZUW0K4mAbiwWtuf0uxFAgA7
 --abcd--"'
-test_emacs "(notmuch-show \"id:${gen_msg_id}\")
-	    (test-output)"
-# Normalize output for Emacs 23 and Emacs 24
-sed -i 's/\[cid\]/*/' OUTPUT
-cat <<EOF >EXPECTED
-Notmuch Test Suite <test_suite@notmuchmail.org> (2001-01-05) (inbox)
-Subject: HTML mail with images
-To: Notmuch Test Suite <test_suite@notmuchmail.org>
-Date: Fri, 05 Jan 2001 15:43:57 +0000
-
-[ multipart/related ]
-[ text/html ]
-*
-EOF
-test_expect_equal_file OUTPUT EXPECTED
+test_emacs "(let ((mm-text-html-renderer
+		   (if (assq 'shr mm-text-html-renderer-alist)
+		       'shr 'html2text)))
+	      (notmuch-show \"id:${gen_msg_id}\"))
+	    (test-output)" > /dev/null
+# Different Emacs versions and renderers give very different results,
+# so just check that something reasonable showed up.
+test_expect_success "Rendering HTML mail with images" \
+    'grep -q smiley OUTPUT'
 
 
 test_done