smurf: Create itermap *after* the map quality has been created.

Previously, each itermap has the quality values associated with the
previous iteration rather than the current iteration.
smurf: Correct ordering of the axes in the time series WCS

Previously, the WCS always assumed the time axis was the third axis,
regarles of whether the array has been transposed or not. Now, the WCS
axes are permuted along with the data array.
smurf: Correct AST masking for single-sample pixels

The AST model was being masked in two differnt ways at two different
places, leading to inconsistencies for map pixels that receive a single
data sample. Such pixels have a good data value but a bad variance.
smurf: Clear up some compiler warnings