enable mhtml-mode by default

* lisp/files.el (auto-mode-alist): Reference mhtml-mode, not
html-mode.
(magic-fallback-mode-alist): Likewise.
* lisp/net/eww.el (eww-view-source): Use mthml-mode.

lisp/files.el

@@ -2429,7 +2429,7 @@ since only a single case-insensitive search through the alist is made."
    (lambda (elt)
      (cons (purecopy (car elt)) (cdr elt)))
    `(;; do this first, so that .html.pl is Polish html, not Perl
-     ("\\.[sx]?html?\\(\\.[a-zA-Z_]+\\)?\\'" . html-mode)
+     ("\\.[sx]?html?\\(\\.[a-zA-Z_]+\\)?\\'" . mhtml-mode)
      ("\\.svgz?\\'" . image-mode)
      ("\\.svgz?\\'" . xml-mode)
      ("\\.x[bp]m\\'" . image-mode)
@@ -2791,8 +2791,8 @@ If FUNCTION is nil, then it is not called.  (That is a way of saying
 		comment-re "*"
 		"\\(?:!DOCTYPE[ \t\r\n]+[^>]*>[ \t\r\n]*<[ \t\r\n]*" comment-re "*\\)?"
 		"[Hh][Tt][Mm][Ll]"))
-     . html-mode)
-    ("<!DOCTYPE[ \t\r\n]+[Hh][Tt][Mm][Ll]" . html-mode)
+     . mhtml-mode)
+    ("<!DOCTYPE[ \t\r\n]+[Hh][Tt][Mm][Ll]" . mhtml-mode)
     ;; These two must come after html, because they are more general:
     ("<\\?xml " . xml-mode)
     (,(let* ((incomment-re "\\(?:[^-]\\|-[^-]\\)")

lisp/net/eww.el

@@ -641,8 +641,11 @@ Currently this means either text/html or application/xhtml+xml."
             (when (coding-system-p cs)
               (decode-coding-region (point-min) (point-max) cs)
               (setq buffer-file-coding-system last-coding-system-used))))
-	(when (fboundp 'html-mode)
-	  (html-mode))))
+        (cond
+         ((fboundp 'mhtml-mode)
+          (mhtml-mode))
+         ((fboundp 'html-mode)
+	  (html-mode)))))
     (view-buffer buf)))
 
 (defun eww-toggle-paragraph-direction ()