Rework locking in store.lisp.
Rework locking in store.lisp.

Store functions are now protected by *VM-LOCK*, not by interrupts &
spinlocks. ALLOC & FREE require *VM-LOCK* to be held before calling.

The recent swap changes have made the pager & snapshot threads the only
threads to call the store functions, so complex page-fault-safe locking
is no longer required.

AugustusHuang/Mezzano,varjagg/Mezzano,froggey/Mezzano,rvedam/Mezzano,froggey/Mezzano,rvedam/Mezzano,AugustusHuang/Mezzano,varjagg/Mezzano