Fixed two memory reclamation problems:
Fixed two memory reclamation problems:

1. Need to update the consumed field, otherwise vspace library leaks memory.

2. Have every domain keep up to 1MB of free memory around as fast reserve,
   before returning to memory server. This circumvents a problem with
   asynchronous memory reclamation: If memory is allocated and freed in a
   tight loop, allocating memory happens faster than it will be freed
   (freeing is an asynchronous operation). This commit works on the
   assumption that allocating and then freeing more than 1MB in a tight loop
   is not something one does regularly. Also, keeping a little bit of memory
   as local reserve should speed up fine-grain memory management.

8l/barrelfish,linusyang/barrelfish,kishoredbn/barrelfish,mslovy/barrelfish,linusyang/barrelfish,BarrelfishOS/barrelfish,8l/barrelfish,mslovy/barrelfish,linusyang/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,8l/barrelfish,utsav2601/cmpe295A,utsav2601/cmpe295A,BarrelfishOS/barrelfish,8l/barrelfish,kishoredbn/barrelfish,mslovy/barrelfish,linusyang/barrelfish,utsav2601/cmpe295A,mslovy/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,8l/barrelfish,utsav2601/cmpe295A,linusyang/barrelfish,utsav2601/cmpe295A,mslovy/barrelfish,BarrelfishOS/barrelfish,utsav2601/cmpe295A,kishoredbn/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,8l/barrelfish,mslovy/barrelfish,kishoredbn/barrelfish