ACL support for ext2/3

The following patch set adds ACL support to the ext2/3 filesystem. It is a port of the 0.8.50 patches from Andreas Gruenbacher. It requires the Extended Attribute patches which I had sent earlier as a pre-requisite, and represents the 2nd of 3 sets of patches from the acl.bestbits.at code. (The first set was the EA patches; this is the second set of patches; and the third set of patches adds ACL support to NFS, so that the NFS server respects the ACL set on the filesystem.)

Some of these patches in this set are shared in common with the XFS filesystem, and are needed for ACL support in XFS as well. These patches are versus 2.5.40, and still reflect the original design decision of allowing ext2 and ext3 ACL support to be available as separate standalone modules. (See the discussion of the EA patches about whether or not this makes sense.)

Please comment/bleed on these patches.

- Ted