Added change for MATH-817.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1459886 13f79535-47bb-0310-9956-ffa450edef68
Improved speed of FastMath copysign methods.

JIRA: MATH-951

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1459887 13f79535-47bb-0310-9956-ffa450edef68