Normalize remote IP addresses when writing to logs, etc

Summary:
Ref T11939. IPv4 addresses can normally only be written in one way, but IPv6 addresses have several formats.

For example, the addresses "FFF::", "FfF::", "fff::", "0ffF::", "0fFf:0::", and "0FfF:0:0:0:0:0:0:0" are all the same address.

Normalize all addresses before writing them to logs, etc, so we store the most-preferred form ("fff::", above).

Test Plan:
Ran an SSH clone over IPv6:

```
$ git fetch ssh://local@::1/diffusion/26/locktopia.git
```

It worked; verified that address read out of `SSH_CLIENT` sensibly.

Faked my remote address as a non-preferred-form IPv6 address using `preamble.php`.

Failed to login, verified that the preferred-form version of the address appeared in the user activity log.

Made IPv6 requests over HTTP:

```
$ curl -H "Host: local.phacility.com" "http://[::1]/"
```

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11939

Differential Revision: https://secure.phabricator.com/D16987

src/applications/people/storage/PhabricatorUserLog.php

@@ -108,18 +108,28 @@ final class PhabricatorUserLog extends PhabricatorUserDAO
     $log->setUserPHID((string)$object_phid);
     $log->setAction($action);
 
-    $log->remoteAddr = (string)idx($_SERVER, 'REMOTE_ADDR', '');
+    $address = PhabricatorEnv::getRemoteAddress();
+    if ($address) {
+      $log->remoteAddr = $address->getAddress();
+    } else {
+      $log->remoteAddr = '';
+    }
 
     return $log;
   }
 
   public static function loadRecentEventsFromThisIP($action, $timespan) {
+    $address = PhabricatorEnv::getRemoteAddress();
+    if (!$address) {
+      return array();
+    }
+
     return id(new PhabricatorUserLog())->loadAllWhere(
       'action = %s AND remoteAddr = %s AND dateCreated > %d
         ORDER BY dateCreated DESC',
       $action,
-      idx($_SERVER, 'REMOTE_ADDR'),
-      time() - $timespan);
+      $address->getAddress(),
+      PhabricatorTime::getNow() - $timespan);
   }
 
   public function save() {