retry to read the sent request a few times if it doesn't exist the first time

tests/runtests.pl

@@ -1161,8 +1161,22 @@ sub singletest {
     }
 
     if(@protocol) {
-        # verify the sent request
-        my @out = loadarray($SERVERIN);
+        my @out;
+        my $retry = 5;
+
+        # Verify the sent request. Sometimes, like in test 513 on some hosts,
+        # curl will return back faster than the server writes down the request
+        # to its file, so we might need to wait here for a while to see if the
+        # file gets written a bit later.
+
+        while($retry--) {
+            @out = loadarray($SERVERIN);
+
+            if(!$out[0]) {
+                # nothing there yet, wait a while and try again
+                sleep(1);
+            }
+        }
 
         # what to cut off from the live protocol sent by curl
         my @strip = getpart("verify", "strip");