Fix for U4-5564

If umbracoUseSSL is set to true, change makes GetCurrentServerUmbracoBaseUrl() return HTTPS URL.  Also overrides ApplicationContext.Current.OriginalRequestUrl to use Port 443 instead of originally loaded port.
I'd have to go back into Visual Studio again to make sure, but my recollection is that without this line Umbraco tried doing the scheduled requests at https://mywebsite:80.  I'm trying to remember if there is a reason why I didn't just drop the port number out entirely.  Is there (should there be?) a config variable for specifying non-standard ports used?