I have added the 2.6.29 support and it appears to do what is required. 
Feedback appreciated.

The use of grab_cache_page_write_begin has been backported to 2.6.28 so for 
more recent subreleases of 2.6.28. There are no useful kernel version 
identifiers for the releases between 2.6.28 and 2.6.29 so you will need to 
hack the appropriate lines manually.

-- Charles