fix test_geodtest_geodesic_direct12 S12 behavior

[stonylohr]

This unit test for the direct method using GeodTest data currently requires a tolerance of up to 20000 to accept results found for the S12 value. Investigate, presumably fix geodesic behavior, and adjust the S12 tolerance in this test to a more reasonable level.

Also, confirm that this addresses S12 behavior in test_geodtest_geodesic_direct21, and adjust its tolerance. I expect the same bug(s) affect both tests.