The volume TTL and file TTL are not necessarily the same. as long as
file TTL is smaller than volume TTL, it'll be fine.
volume TTL is used when assigning file id, e.g.
http://.../dir/assign?ttl=3h
file TTL is used when uploading
change replication_type to ReplicaPlacement, hopefully cleaner code
works for 9 possible ReplicaPlacement
xyz
x : number of copies on other data centers
y : number of copies on other racks
z : number of copies on current rack
x y z each can be 0,1,2
Minor:
weed server "-mdir" default to "-dir" if empty
