smurf: Always use same map size on every iteration in skyloop

This is necessary now that the LUT model is cached, since changes in the
data flagging on each iteration (steps, spikes etc) can result in small
changes of the default map size, which would then invalidate the
comntents of the cached LUT model.
ast: Debug facility to list all memory blocks if limit is exceeded

Dump details of all active memory blocks if the total memory allocation
specified by astMemoryWarning is exceeded. Only available if compiled
with memdebug.
ast: Fix apparent memory leak

Not a real memory leak, since it is a one-off memory allocation.
smurf: Fix memory leaks
smurf: Fix estimation of required memory

The memory needed by the NOI model depends on the NOI.BOX_SIZE parameter.
smurf: No need to allocate memory for the AST model

The AST model is determiend from the current map, and so we do not need
to allocate extra memory to hold it.