Allow ".ico" files to be viewed

Summary: No reason to keep these out of the defaults, can be useful in web stuff.

Test Plan: Uploaded, viewed a .ico file.

Reviewers: btrahan, paularmstrong

Reviewed By: btrahan

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1883

conf/default.conf.php

@@ -531,6 +531,12 @@ return array(
     'image/png'   => 'image/png',
     'image/gif'   => 'image/gif',
     'text/plain'  => 'text/plain; charset=utf-8',
+
+    // ".ico" favicon files, which have mime type diversity. See:
+    // http://en.wikipedia.org/wiki/ICO_(file_format)#MIME_type
+    'image/x-ico'               => 'image/x-icon',
+    'image/x-icon'              => 'image/x-icon',
+    'image/vnd.microsoft.icon'  => 'image/x-icon',
   ),
 
   // Phabricator can proxy images from other servers so you can paste the URI