Comment 3 for bug 1026337

This is probably the same misbehaviour I've just started exploring. I'm attaching a partial fix. (Partial because it some what solved my test case but not completely.)

Anyway, function comment for pcbnew/drc_clearance_test_functions.cpp:DRC::checkMarginToCircle says that this function should have >= behaviour, but one of the tests uses > behaviour. I've corrected this and it improves DRC-correctness.