Towns with only inactive successors

[jdesboeufs]

Many towns have an end_datetime but inactive successors. 1319 town records may be in this situation.

Example (Arlod):

cat data/towns.csv | grep COM01033@1942-01-01

COM01018@1942-01-01,01018,1942-01-01 00:00:00,1970-12-31 23:59:59,Arlod,COM01033@1942-01-01,,DEP01@1860-07-01,NULL,310
COM01033@1942-01-01,01033,1942-01-01 00:00:00,1956-10-18 23:59:59,Bellegarde,COM01033@1956-10-19,COM01018@1942-01-01,DEP01@1860-07-01,NULL,100
COM01033@1956-10-19,01033,1956-10-19 00:00:00,9999-12-31 23:59:59,Bellegarde-sur-Valserine,,COM01033@1942-01-01;COM01126@1942-01-01,DEP01@1860-07-01,11644,0