VFS fileop cleanups by collapsing AIO and vector IO

Hi Andrew,

Here the VFS cleanup patches to collapse vector and AIO fileop
methods + cleanups to filemap.c against 2.6.17.

These series of patches clean up and streamlines generic_file_*
interfaces in filemap.c.

BTW, I dropped adding vector-aio support (aio.c) patch for now
as it can be added later.

===
These patches collapses all the vectored IO support into 
single set of file-operation method using aio_read/aio_write.
Last patch (3) sets all thefilesystems .read/.write/.aio_read/
.aio_write methods correctly to allow us to cleanup most
generic_file_*_read/write interfaces in filemap.c

After this patch set, we should end up with ONLY following
read/write (exported) interfaces in filemap.c:

        generic_file_aio_read() - read handler
        generic_file_aio_write() - write handler
        generic_file_aio_write_nolock() - no lock write handler

Here is the summary:

[PATCH 1/3] Vectorize aio_read/aio_write fileop methods

[PATCH 2/3] Remove readv/writev methods and use aio_read/aio_write
instead.

[PATCH 3/3] Streamline generic_file_* interfaces and filemap cleanups

Thanks,
Badari