Add support for multiple block allocation in ext3-get-blocks().

Look up the disk block mapping and count the total number of blocks to
allocate, then pass it to ext3_new_block(), where the real block allocation is
performed.  Once multiple blocks are allocated, prepare the branch with those
just allocated blocks info and finally splice the whole branch into the block
mapping tree.
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>