JDK 9 RFR of JDK-8139688 Port fdlibm exp to Java

[joe darcy]

Hello,

Next up in porting fdlibm to Java after cbrt (JDK-8136799), pow 
(JDK-8134795) and hypot (JDK-7130085) earlier in JDK 9 is exp:

    JDK-8139688 Port fdlibm exp to Java
    http://cr.openjdk.java.net/~darcy/8139688.5/

Same methodology followed as when porting the earlier functions.

Thanks,

-Joe