Add "harvest" test

[MaximeVdB]

At last, here's the Harvest test, together with the bugfixes required to make it pass.

Performed tests (all with DEBUG=1, and with both FORTRAN_EXE=0 and FORTRAN_EXE=1, and with both the Singularity image and with foss-2018a):

• selected Europe pixels (~50 of them),
• the Perennial test,
• the harvest test itself of course.