Fix `org-paste-subtree'

* lisp/org.el (org-paste-subtree): Use `org-outline-regexp-bol'.

The function cannot detect the proper level when a headline around
point contains spurious white spaces after the stars.

lisp/org.el

@@ -8536,7 +8536,6 @@ When REMOVE is non-nil, remove the subtree from the clipboard."
   (org-with-limited-levels
    (let* ((visp (not (org-invisible-p)))
 	  (txt tree)
-	  (^re_ "\\(\\*+\\)[  \t]*")
 	  (old-level (if (string-match org-outline-regexp-bol txt)
 			 (- (match-end 0) (match-beginning 0) 1)
 		       -1))
@@ -8553,7 +8552,7 @@ When REMOVE is non-nil, remove the subtree from the clipboard."
 			    (condition-case nil
 				(progn
 				  (outline-previous-visible-heading 1)
-				  (if (looking-at ^re_)
+				  (if (looking-at org-outline-regexp-bol)
 				      (- (match-end 0) (match-beginning 0) 1)
 				    1))
 			      (error 1))))
@@ -8562,7 +8561,7 @@ When REMOVE is non-nil, remove the subtree from the clipboard."
 			    (progn
 			      (or (looking-at org-outline-regexp)
 				  (outline-next-visible-heading 1))
-			      (if (looking-at ^re_)
+			      (if (looking-at org-outline-regexp-bol)
 				  (- (match-end 0) (match-beginning 0) 1)
 				1))
 			  (error 1))))