ocfs2: Support creation of unwritten extents

This can now be trivially supported with re-use of our existing extend code.

ocfs2_allocate_unwritten_extents() takes a start offset and a byte length
and iterates over the inode, adding extents (marked as unwritten) until len
is reached. Existing extents are skipped over.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

diff --cc fs/ocfs2/alloc.c
Simple merge

diff --cc fs/ocfs2/alloc.h
Simple merge

diff --cc fs/ocfs2/aops.c
Simple merge

diff --cc fs/ocfs2/dir.c
Simple merge

diff --cc fs/ocfs2/file.c
Simple merge

diff --cc fs/ocfs2/file.h
Simple merge

diff --cc fs/ocfs2/namei.c
Simple merge