When testing the calculated longitude, we must *multiply* the angular
error with a factor derived from the latitude, and we must pass the
latitude in *radians* to the cos function.
For the "LVermGeo RLP Pruem GK2" dataset, the error is slightly larger
than expected, so we need to increase the tolerance as well.

All tests pass with PROJ 4.9.3 (Ubuntu 18.04).
Task: GH-1325 (Geographic offset in CH1903+/LV95 with PROJ 6)

...instead of 'PROJ.4'.

User interface and user documentation need to be handled later.

The file format usage of 'PROJ.4 as an identifier will need more
thought: The legacy specs need to be supported for handling existing
maps, but PROJ now encourages specifying CRS as AUTHORITY:CODE or
by WKT strings instead of PROJ strings (cf.
https://proj.org/development/migration.html)

This matches the minimum version documented in INSTALL.md.

We can encapsulate the PROJ lib access and memory management
in a simple data type. This will facilitate providing a second
implementation for the new PROJ API.

The Android file handler is supported only for the new API now,
because we are not going to ship an old PROJ version again.