Add support to mirror non package installer files

http/http.go

@@ -3,6 +3,7 @@ package http
 
 import (
 	"fmt"
+	"net/url"
 )
 
 // Error is download error connected to HTTP code
@@ -15,3 +16,13 @@ type Error struct {
 func (e *Error) Error() string {
 	return fmt.Sprintf("HTTP code %d while fetching %s", e.Code, e.URL)
 }
+
+// NoCandidateFoundError indicates that now candidate of given url could be found
+type NoCandidateFoundError struct {
+	URL *url.URL
+}
+
+// Error message
+func (e *NoCandidateFoundError) Error() string {
+	return fmt.Sprintf("no candidates for %s found", e.URL)
+}