Capture: Fix the case of using a template file

* lisp/org-capture.el (org-capture-set-plist): Make sure txt is a string
before calling `string-match'.
(org-capture-templates): Fix customization type.

Modified from a patch proposal by Johan Friis.

TINYCHANGE

lisp/org-capture.el

@@ -285,7 +285,7 @@ calendar           |  %:type %:date"
 	   (choice :tag "Template"
 		   (string)
 		   (list :tag "File"
-			 (const :format "" file-contents)
+			 (const :format "" file)
 			 (file :tag "Template file"))
 		   (list :tag "Function"
 			 (const :format "" function)
@@ -981,7 +981,7 @@ Point will remain at the first line after the inserted text."
   (org-capture-put :key (car entry) :description (nth 1 entry)
 		   :target (nth 3 entry))
   (let ((txt (nth 4 entry)) (type (or (nth 2 entry) 'entry)))
-    (when (or (not txt) (not (string-match "\\S-" txt)))
+    (when (or (not (stringp txt)) (not (string-match "\\S-" txt)))
       ;; The template may be empty or omitted for special types.
       ;; Here we insert the default templates for such cases.
       (cond