Fix snapshot policy for legacy clients

For core <2.10, serve updates from snapshots as before (repo_view is
"unknown").

Only HTTP clients sending X-Repo-View header receive the repo view as
the new feature 6970 says (repo_view is "managed" or "latest").

imageroot/script/snapshot.php

@@ -54,7 +54,7 @@ function main() {
         echo "Not found\n";
     }
 
-    $repo_view = isset($_SERVER['HTTP_X_REPO_VIEW']) ? $_SERVER['HTTP_X_REPO_VIEW'] : "latest";
+    $repo_view = isset($_SERVER['HTTP_X_REPO_VIEW']) ? $_SERVER['HTTP_X_REPO_VIEW'] : "unknown";
     $username = isset($_SERVER['PHP_AUTH_USER']) ? $_SERVER['PHP_AUTH_USER'] : "";
     $password = isset($_SERVER['PHP_AUTH_PW']) ? $_SERVER['PHP_AUTH_PW'] : "";
 
@@ -70,13 +70,13 @@ function main() {
             }
             $snapshot = array_pop($lsnapshots);
         }
-    } else if (substr($_SERVER['DOCUMENT_URI'], 0, 10) == "/distfeed/") {
+    } else if ($repo_view != "unknown" && substr($_SERVER['DOCUMENT_URI'], 0, 10) == "/distfeed/") {
         // Access to latest metadata (distfeed) if client is not
         // authenticated, or if the request comes from the user through
         // the Software Center APIs.
         $snapshot = 'head';
     } else {
-        // Access to latest DNF mirror contents.
+        // Access to snapshot contents.
         $snapshot = array_pop($lsnapshots);
     }