Preliminary review: Adding tracing of I/O calls

[Staffan Larsen]

This is a preliminary review request for adding an API for tracing I/O calls. For now, this is an empty infrastructure intended to enable diagnosing/tracing of i/o calls. A user of the API can register a listener and get callbacks for read and write operations on sockets and files. It does not (yet) cover asynchronous i/o calls. When not used, the implementation should add a minimum of overhead. To provide useful information to the user, FileInputStream, FileOutputStream and RandomAccessFile have been modified to keep track of the path they operate on (when available).

Webrev: http://cr.openjdk.java.net/~sla/iotrace/webrev.00/

Feedback is most welcome,
/Staffan