tweak(beancount): include directives for next/prev transaction

+beancount/next-transaction and +beancount/previous-transaction would
formerly skip timestampped directives, e.g.

  2016-09-15 * "Foo" ""
    Expenses:Y                                  779.00 DKK
    Assets:X:Checkings
  2016-11-16 balance Assets:X:Checkings         8,417.58 DKK
  2016-12-13 * "Bar" ""
    Assets:X:Checkings                          2,100.00 DKK
    Income:Z

The `balance` directive would be skipped over. This commit changes that
to include them. Perhaps the commands should be renamed to
+beancount/{next,previous}-entry to better reflect my intended purpose
for them?

modules/lang/beancount/autoload.el

@@ -172,12 +172,19 @@ Updates the date to today."
 (defun +beancount/next-transaction (&optional count)
   "Jump to the start of the next COUNT-th transaction."
   (interactive "p")
-  (dotimes (_ (or count 1))
-    (beancount-goto-next-transaction)))
+  (let ((beancount-transaction-regexp
+         ;; Don't skip over timestamped directives (like balance or event
+         ;; declarations).
+         (concat beancount-timestamped-directive-regexp
+                 "\\|" beancount-transaction-regexp)))
+    (dotimes (_ (or count 1))
+      (beancount-goto-next-transaction))))
 
 ;;;###autoload
 (defun +beancount/previous-transaction (&optional count)
   "Jump to the start of current or previous COUNT-th transaction."
   (interactive "p")
   (re-search-backward
-   beancount-transaction-regexp nil t (or count 1)))
+   (concat beancount-timestamped-directive-regexp
+           "\\|" beancount-transaction-regexp)
+   nil t))