Fix Caching Problem in 0.16.3

This fixes the caching problem

  http://golem.ph.utexas.edu/instiki/show/Known+Bugs?rev=13#Caching

which afflicts some installations of 0.16.3. With the patch, it's no
longer necessary that the Instiki directory be owned by the instiki
user (yay!).

vendor/rails/activesupport/lib/active_support/core_ext/file/atomic.rb

@@ -27,7 +27,7 @@ module ActiveSupport #:nodoc:
             old_stat = stat(file_name)
           rescue Errno::ENOENT
             # No old permissions, write a temp file to determine the defaults
-            check_name = ".permissions_check.#{Thread.current.object_id}.#{Process.pid}.#{rand(1000000)}"
+            check_name = join(dirname(file_name), ".permissions_check.#{Thread.current.object_id}.#{Process.pid}.#{rand(1000000)}")
             open(check_name, "w") { }
             old_stat = stat(check_name)
             unlink(check_name)