Fix for blocker bug 126770 (Undo/Redo doesn't work in Text widgets, Composer, and Mail)

mozilla/editor/txmgr/src/nsTransactionManager.cpp
  mozilla/editor/txmgr/src/nsTransactionStack.cpp

    - nsTransactionStack::Peek() was intended to return NULL for
      an empty stack so I changed timeless' change for bug 114166
      to return NS_OK and init the return value to zero.

    - timeless also changed the behavior of nsDeque::End(), it no
      longer returns an interator that is one past the end. So
      nsTransactionStack::Peek() had to call CurrentItem() instead
      of operator--.

    - I also backed out the changes made to nsTransactionManager.cpp
      cause they are unnecessary with the changes made to
      nsTransactionStack::Peek() above.

r=timeless@bemail.org  sr=hyatt@netscape.com  a=leaf@mozilla.org

editor/txmgr/src/nsTransactionManager.cpp

@@ -482,9 +482,6 @@ nsTransactionManager::SetMaxTransactionCount(PRInt32 aMaxCount)
 
   LOCK_TX_MANAGER(this);
 
-  result = mDoStack.GetSize(&total);
-  if (NS_SUCCEEDED(result) && total) {
-
   // It is illegal to call SetMaxTransactionCount() while the transaction
   // manager is executing a  transaction's DoTransaction() method because
   // the undo and redo stacks might get pruned! If this happens, the
@@ -502,7 +499,6 @@ nsTransactionManager::SetMaxTransactionCount(PRInt32 aMaxCount)
     UNLOCK_TX_MANAGER(this);
     return NS_ERROR_FAILURE;
   }
-  }
 
   // If aMaxCount is less than zero, the user wants unlimited
   // levels of undo! No need to prune the undo or redo stacks!

editor/txmgr/src/nsTransactionStack.cpp

@@ -101,14 +101,12 @@ nsTransactionStack::Peek(nsTransactionItem **aTransaction)
   if (!aTransaction)
     return NS_ERROR_NULL_POINTER;
 
-  if (!mQue.GetSize())
-    return NS_ERROR_NULL_POINTER;
+  if (!mQue.GetSize()) {
+    *aTransaction = 0;
+    return NS_OK;
+  }
 
-  /* nsDeque's End() method returns an iterator that is
-   * passed the last entry of the deque. We need to decrement
-   * to get to the last entry.
-   */
-  *aTransaction = (nsTransactionItem *)(--mQue.End());
+  *aTransaction = (nsTransactionItem *)(mQue.End().GetCurrent());
 
   return NS_OK;
 }