emacs: fix notmuch-search-line-faces defcustom

In commit 2a7b11b064 the default value
for notmuch-search-line-faces was changed so that it didn't match the
specification in the corresponding defcustom. This meant that it was
difficult for the user to customize this variable as they got a type
mismatch error.

Note anyone who had already customised this variable would not see
this bug as their customisation would match the defcustom.

emacs/notmuch.el

@@ -669,9 +669,16 @@ of the result."
 		  (goto-char (point-min))
 		  (forward-line (1- notmuch-search-target-line)))))))))
 
+(define-widget 'notmuch--custom-face-edit 'lazy
+  "Custom face edit with a tag Edit Face"
+  ;; I could not persuage custom-face-edit to respect the :tag
+  ;; property so create a widget specially
+  :tag "Manually specify face"
+  :type 'custom-face-edit)
+
 (defcustom notmuch-search-line-faces
-  '(("unread" 'notmuch-search-unread-face)
-    ("flagged" 'notmuch-search-flagged-face))
+  '(("unread" . notmuch-search-unread-face)
+    ("flagged" . notmuch-search-flagged-face))
   "Alist of tags to faces for line highlighting in notmuch-search.
 Each element looks like (TAG . FACE).
 A thread with TAG will have FACE applied.
@@ -689,7 +696,9 @@ matching tags are merged, with earlier attributes overriding
 later. A message having both \"deleted\" and \"unread\" tags with
 the above settings would have a green foreground and blue
 background."
-  :type '(alist :key-type (string) :value-type (custom-face-edit))
+  :type '(alist :key-type (string)
+		:value-type (radio (face :tag "Face name")
+				    (notmuch--custom-face-edit)))
   :group 'notmuch-search
   :group 'notmuch-faces)