(stable) Discard stdout/stderr from the aphlict subprocess when running in daemon (normal) mode

Summary:
Fixes T11818. We don't discard output, so once we read more than 2GB of output we'll exceed the maximum size of a string in an internal buffer.

Instead, configure the future so output is discarded.

Test Plan: Added logging to `libphutil/`, saw internal buffer grow steadily before this change and stay constant at 0 after this change.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11818

Differential Revision: https://secure.phabricator.com/D16855

src/applications/aphlict/management/PhabricatorAphlictManagementWorkflow.php

@@ -416,6 +416,14 @@ abstract class PhabricatorAphlictManagementWorkflow
       while (true) {
         global $g_future;
         $g_future = new ExecFuture('exec %C', $command);
+
+        // Discard all output the subprocess produces: it writes to the log on
+        // disk, so we don't need to send the output anywhere and can just
+        // throw it away.
+        $g_future
+          ->setStdoutSizeLimit(0)
+          ->setStderrSizeLimit(0);
+
         $g_future->resolve();
 
         // If the server exited, wait a couple of seconds and restart it.