Add missing parameter to strncasecmp()

Summary:
strncasecmp() takes 3 parameters, not 2. This worked in the general case because we usually do not set any headers, so we don't enter this comparison block. However, now that we set `User-Agent` from OAuth it is complaining in the logs.

  [13-May-2013 16:51:28] WARNING: [pool www] child 28977 said into stderr: "NOTICE: PHP message: [2013-05-13 16:51:28] ERROR 2: strncasecmp() expects exactly 3 parameters, 2 given at [/core/libphutil/src/future/http/HTTPSFuture.php:172]"
  [13-May-2013 16:51:28] WARNING: [pool www] child 28977 said into stderr: "NOTICE: PHP message:   #0 strncasecmp(User-Agent, Expect) called at [/core/libphutil/src/future/http/HTTPSFuture.php:172]"
  [13-May-2013 16:51:28] WARNING: [pool www] child 28977 said into stderr: "NOTICE: PHP message:   #1 HTTPSFuture::isReady() called at [/core/libphutil/src/future/Future.php:40]"
  [13-May-2013 16:51:28] WARNING: [pool www] child 28977 said into stderr: "NOTICE: PHP message:   #2 Future::resolve() called at [/core/libphutil/src/future/http/BaseHTTPFuture.php:231]"
  [13-May-2013 16:51:28] WARNING: [pool www] child 28977 said into stderr: "NOTICE: PHP message:   #3 BaseHTTPFuture::resolvex() called at [/core/phabricator/src/applications/auth/controller/PhabricatorOAuthLoginController.php:55]"
  [13-May-2013 16:51:28] WARNING: [pool www] child 28977 said into stderr: "NOTICE: PHP message:   #4 PhabricatorOAuthLoginController::processRequest() called at [/core/phabricator/webroot/index.php:84]"

Test Plan: Verified strncasecmp() behavior.

Reviewers: btrahan, chad

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D5917