Fix for bz 142849
    
    When you do gfs_write on a stuffed inode, you don't update the page cache,
    because the inodes are stored in the buffer cache. This doesn't effect reads,
    because gfs special cases the stuffed reads.  Unfortunately, sendfile needs to
    use the page cache, because it relys on the destination socket's sendpage
    routine to work. So my fix is: after you do a write on a stuffed inode, if the
    first page of the file is cached (It appears from looking at the code that
    there is already an assumption that stuffed inodes will never be more than a
    page in length) mark the cached page as not uptodate.