Change of idea: instead of storing `date_index` and `ishape_last` in a
file `contents.csv`, store only `ishape_last` in a file
`ishape_last.txt`. The `date_index` column was useless and it
complicated reading the file. The first value of `date_index` can be
read from one of the three DBF files. Also, to roll with the flow, let
the lower bound of `ishape_last` in main unit `test_overlap` be 1
instead of k1.

Change order of actual arguments of `dbf_read_attribute_03` following
revision of `Shapelib_03`.