document wxProgressDialog::Update(maximumValue) behaviour and warn the user that it may generate unwanted re-entrancies because of wxDialog::ShowModal()

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@59431 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/dialog.h

@@ -586,6 +586,7 @@ public:
         Note that this function creates a temporary event loop which takes
         precedence over the application's main event loop (see wxEventLoopBase)
         and which is destroyed when the dialog is dismissed.
+        This also results in a call to wxApp::ProcessPendingEvents().
 
         @return The value set with SetReturnCode().