[Therion] Length & Depth differ

[Bruce]

>(I presume the lists always report on the whole
survey, not just the exported map -untested).

After some testing I conclude that the list exports DO report on the entire
'source' survey, regardless of the 'select'ed maps to be exported.  Have not
checked the numbers are added correctly however. (The numbers still differ
between list and pdf).

The map outputs, when NO 'map' is 'select'ed, correctly produce a pdf with
each defined map on a separate layer when the projection is 'plan'.
When the projection is 'elevation 290 deg' only one of the defined maps is
exported (only about half of the cave in this case). This dataset works fine
when maps are explicitly 'select'ed.  Seems the default behaviour might be
broken for elevations.

Bruce