Interface for verifying fetch file selection (see MGFetch.h) If MMGFetchVerifier is passed to MGFetch then VerifySelectionL is called when user tries to select file(s) from the fetcher. If VerifySelectionL returns ETrue then the fetcher popup is closed and the selection is accepted. If VerifySelectionL returns EFalse then the fetcher is not closed and user needs to select different file(s) or cancel the operation.