[UPDATED RFC] Create with EA initial work

[Niv Sardi <xaiki@sgi.com>]

Thanks to everyone for the review of the former patchset, this ones
fixes the bugs found by dgc, changes the naming of the *_trans_*
functions, splits out xfs_bmap_add_attrfork{,_trans} to have one
version doing the whole allocation and calling into the other as
suggested by hch, and has the x_t -> struct x changes too.

There is a bug in this, that I can see with the Parent Pointers code
going on top of it (that will be posted soon), it is basically calling
xfs_attr_set_int_trans() in xfs_create() just before the last
commit. For some reason, the first call to xfs_roll_trans (after
xfs_bmap_add_attrfork_trans()) will complain about the inode being
unlocked after xfs_trans_commit(). I understand I need to call
xfs_trans_ihold(ip) on it, but we already do in xfs_create() so I
think I must be missing something else… any ideas ?