Fixed an issue with noisy functions for ODE events detection.

The issue was not detected in Apache Commons Math but in similar code in
Orekit (see https://www.orekit.org/forge/projects/orekit/issues/160).

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1558462 13f79535-47bb-0310-9956-ffa450edef68