Index: includes/file.mimetypes.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/file.mimetypes.inc,v
retrieving revision 1.2
diff -u -r1.2 file.mimetypes.inc
--- includes/file.mimetypes.inc	11 Jun 2009 04:39:50 -0000	1.2
+++ includes/file.mimetypes.inc	16 Jul 2009 00:19:52 -0000
@@ -484,7 +484,7 @@
       'pfb' => 113,
       'pcf' => 113,
       'gsf' => 113,
-      'pcf.Z' => 113,
+      'pcf.z' => 113,
       'mm' => 114,
       'spl' => 115,
       'gnumeric' => 116,
Index: includes/file.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/file.inc,v
retrieving revision 1.174
diff -u -r1.174 file.inc
--- includes/file.inc	10 Jul 2009 04:08:20 -0000	1.174
+++ includes/file.inc	16 Jul 2009 00:19:51 -0000
@@ -1554,7 +1571,7 @@
   //   - image.jpeg, and
   //   - awesome.image.jpeg
   while ($additional_part = array_pop($file_parts)) {
-    $extension = $additional_part . ($extension ? '.' . $extension : '');
+    $extension = strtolower($additional_part . ($extension ? '.' . $extension : ''));
     if (isset($mapping['extensions'][$extension])) {
       return $mapping['mimetypes'][$mapping['extensions'][$extension]];
     }