Revert "Revert "make the "FILE" property non-special when resolving bibtex values""

This reverts commit 4b423ac3cb6ae06e5be649e8a4b6c75bfb9f5c12.

lisp/org-bibtex.el

@@ -278,8 +278,11 @@ This variable is relevant only if `org-bibtex-export-tags-as-keywords` is t."
 ;;; Utility functions
 (defun org-bibtex-get (property)
   ((lambda (it) (when it (org-babel-trim it)))
-   (or (org-entry-get (point) (upcase property))
-       (org-entry-get (point) (concat org-bibtex-prefix (upcase property))))))
+   (let ((org-special-properties
+	  (delete "FILE" (copy-sequence org-special-properties))))
+     (or
+      (org-entry-get (point) (upcase property))
+      (org-entry-get (point) (concat org-bibtex-prefix (upcase property)))))))
 
 (defun org-bibtex-put (property value)
   (let ((prop (upcase (if (keywordp property)