Ignore extN files copied into tree from kernel.

Ignore extN files copied into tree from kernel.
Add extN patches:
- ext3-ino_sb-macro.diff: abstracts access to u.ext3_{sb,i} because we do
  not have a u.extN_{sb,i} in the inode struct and we need to use u.generic.
  This patch is generic and could be included in the stock kernel (2.5 already
  has this abstraction)
- extN-ino_sb-fixup.diff: use the u.generic_{ip,sbp} pointer instead of extN,
  a few bits of cleanup from the above patch related to the hashed directory
  changes, and includes the extN_bread() export which we will no longer need
  to apply to the stock kernel.
- Makefile to do all of the conversion from ext3 to extN and such.