forget to check for write access to kohana logdir

[evoltech]

Failure to do this check causes step 6 of the installer (AllowOverrideChecks) to fail with a misleading message. The following patch to head will fix this:

--- a/installer/steps/ReadWriteAccess.php
+++ b/installer/steps/ReadWriteAccess.php
@@ -45,6 +45,7 @@ class ReadWriteAccess implements IInstallStep
                                     is_writable(dirname(__FILE__)."/../../core/Modules") &&
                                     is_writable(dirname(__FILE__)."/../../core/Cache") &&
                                     is_writable(dirname(__FILE__)."/../../web/application/cache") &&
+                                    is_writable(dirname(__FILE__)."/../../web/application/logs") &&
                                     is_writable(dirname(__FILE__)."/../../web/modules");
         $directoriesCheck->text = $directoriesCheck->result
                 ? "All the directories have the correct permissions."