u-a: Add missing space in --set-selections output

This was lost during the rewrite in C.

debian/changelog

@@ -11,6 +11,7 @@ dpkg (1.16.0) UNRELEASED; urgency=low
   * Add a new --status-logger option to dpkg, similar to --status-fd but
     instead invoke the command ourselves and feed the status information
     to its standard input. Suggested by Raphaël Hertzog.
+  * Add missing space in update-alternative --set-selections output.
 
   [ Raphaël Hertzog ]
   * Fail properly when debian/source/format is empty. Closes: #600854

utils/update-alternatives.c

@@ -1864,7 +1864,7 @@ alternative_set_selection(struct alternative_map *all, const char *name,
 static void
 alternative_set_selections(struct alternative_map *all, FILE* input, const char *desc)
 {
-	const char *prefix = "[" PROGNAME "--set-selections] ";
+	const char *prefix = "[" PROGNAME " --set-selections] ";
 
 	for (;;) {
 		char line[1024], *res, *name, *status, *choice;