Hard-coded check of length of exported survey data as a basic check of ODK...

Hard-coded check of length of exported survey data as a basic check of ODK Briefcase for robustness (in particular for exports from Ethiopia). Currently, 2715 is an expected minimum for Ethiopia. Any small increases in coming weeks are unlikely to lead to not catching an incomplete export. This check is not important for SouthAsia data export which has been reliable. Because of the large data size, this 2715 limit is almost ineffective for South Asia anyway.