RFR: JDK-8023203 - Wrap RandomAccessFile.seek native method into a Java helper method

[Dan Xu]

HiAll,

Please review the simple change for JDK-8023203 - Wrap 
RandomAccessFile.seek native method into a Java helper method. Itadds a 
helper java method and makes it the only place that can invoke the 
native method directly. Thanks!

Webrev: http://cr.openjdk.java.net/~dxu/8023203/webrev/
Bug: http://bugs.sun.com/view_bug.do?bug_id=8023203

-Dan