remove lock and unlock super

Hi all,

I'm trying to remove the functions lock_super/unlock_super and to push the lock into each single fs. Currently these fs use these functions: ext3, ext4, fat, hpfs, exofs, sysv, ufs. At the moment I used the more conservative approach, I created a new mutex s_lock in the private sb info for each fs, so nothing change but a couple of notes:

1) exofs/hpfs: they use lock_super only in one function so the lock seems completely not needed and I removed it, do you see collateral effect?

2) fat/ufs: they have already got functions to lock the fs with a mutex, I don't know at the moment if a general review of the code can give us the possibility to "merge" the locks.

Bugs, comments, review are welcome especially from fs maintainers. Maybe this work can be a first cleaning, after that each fs can adjust its lock policy.

The patch is against 3.6-rc1.

Marco