Fix for weather interpolation problem from Anders Gidenstam

Fix for weather interpolation problem from Anders Gidenstam
Anders said:
With Stuart's help I've looked closer at this and I think I've tracked
down the cause of the problem:
At least on my computer the sort() call on line 234 in
Environment/environment_ctrl.cxx sorts the vector entries by memory
address instead of altitude, i.e. the custom comparison predicate is not
used. This causes the tables of environment conditions to be reordered
into a wrong order at some weather updates, depending, basically,
on where the memory allocator places the objects. (Btw. why are they are
freshly allocated for each update?)