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`.

Organize better the directory `Input`: create sub-directories for regions.

Big change: use SHP triplets that can contain several snapshots. So
program `test_overlap` reads a single SHP triplet. The dates that
`test_overlap` should read are now specified in the input
namelist. SHP triplet directory must now contain a file named
`contents.csv`. `test_overlap` reads `contents.csv` into variables k1
and `ishape_last`. So there is no longer any need to read the number
of entities in one of the shapefiles.

For each region, concatenate SHP triplets for dates 2006/01/01 and
2006/01/02.

Read namelist from process 0 in program `test_send_recv`: it is
simpler since it is the default setting of mpiexec and I do not see
any drawback.

In programs `test_read_snapshot` and `test_send_recv`, just hard code
for now the ishapes we want to read in the SHP triplet.