scoped_allocation: Inherit from persistent_allocation
scoped_allocation: Inherit from persistent_allocation

Make scoped_allocation inherit from persistent_allocation instead. This
has performance benefits for most usages of temporary memory in
Firepony.

nsubtil/lift,nsubtil/lift,chuckseberino/lift,chuckseberino/lift,chuckseberino/lift,nsubtil/lift