RFR 8220238 : Enhancing j.l.Runtime/System::gc specification with an explicit 'no guarantee' statement

[Roger Riggs]

Please review a change to the javadoc of Runtime.gc() and System.gc() to 
clarify
that invoking these methods does not guarantee any specific result or 
timeliness
of completion.

The revised text is:
      * Runs the garbage collector in the Java Virtual Machine.
      *
      * Calling this method suggests that the Java Virtual Machine
      * expend effort toward recycling unused objects in order to
      * make the memory they currently occupy available for reuse
      * by the Java Virtual Machine.
      * There is no guarantee that this effort will recycle any particular
      * number of unused objects, reclaim any particular amount of space,
      * or complete at any particular time, if at all.

Issue:
  https://bugs.openjdk.java.net/browse/JDK-8220238

CSR:
  https://bugs.openjdk.java.net/browse/JDK-8224760

Webrev:
  http://cr.openjdk.java.net/~rriggs/webrev-gc-8220238/index.html

Please review and comment, Roger