This function checks whether the source control plug-in allows multiple checkouts on a file.
The IDE makes two checks to determine if files can be checked out simultaneously by more than one user. First, the source control system must support multiple checkouts. The source control plug-in can specify this capability during initialization by specifying the SCC_CAP_MULTICHECKOUT. Thereafter, as a second check, the IDE calls this function to determine whether or not the current project supports multiple checkouts. If multiple checkouts are supported for the selected project, the plug-in returns a success code and sets pbMultiCheckout to nonzero (TRUE) or FALSE.