The lock.h header contained some hand-crafted lcoking routines from
the pre-SMP days.  In 2.5 only lock_super/unlock_super are left,
guarded by a number of completly unrelated (!) includes.

This patch moves lock_super/unlock_super to fs.h, which defined
struct super_block that is needed for those to operate it, removes
locks.h and updates all caller to not include it and add the missing,
previously nested includes where needed.