(yas-reload-all): Flush the all-parents caches (issue #1194)

* yasnippet.el (yas--flush-all-parents): New function.
(yas-reload-all): Use it.

* yasnippet.el (issue-492-and-494): Don't flush the all=parents cache any
more since `yas-reload-all` does it for us.

yasnippet-tests.el

@@ -1438,7 +1438,6 @@ hello ${1:$(when (stringp yas-text) (funcall func yas-text))} foo${1:$$(concat \
   (yas-with-snippet-dirs '((".emacs.d/snippets"
                             ("yas--test-mode")))
     (yas-reload-all)
-    (put 'c-mode 'yas--all-parents nil)
     (with-temp-buffer
       (let* ((major-mode 'yas--test-mode)
              (expected `(fundamental-mode

yasnippet.el

@@ -824,6 +824,10 @@ which decides on the snippet to expand.")
                             ;; Prevent sharing the tail.
                             (append lists '(()) )))))))
 
+(defun yas--flush-all-parents (mode)
+  (if (get mode 'yas--all-parents)
+      (put mode 'yas--all-parents nil)))
+
 (defun yas--all-parents (mode)
   "Like `derived-mode-all-parents' but obeying `yas--parents'."
   (or (get mode 'yas--all-parents) ;; FIXME: Use `with-memoization'?
@@ -2010,6 +2014,9 @@ prefix argument."
                                (with-current-buffer buffer
                                  yas--editing-template))
                              (buffer-list))))
+
+      (mapatoms #'yas--flush-all-parents)
+
       ;; Warn if there are buffers visiting snippets, since reloading will break
       ;; any on-line editing of those buffers.
       ;;