The command line options

-Xbootclasspath/a:<path>
-Xbootclasspath/p:<path>

have been part of the JDK 1.2 for a long time. They append/prepend a
classpath segment to to the boot classpath. They are needed by the
customer to modify the boot classpath, because the default value of the
boot classpath is not documented and is implementation dependent.

The default classpath happens to be specified in the system property
sun.boot.class.path, but this fact is not documented and is implementation
dependent.

Please
- Choose to make these existing command line options public/supported.
- Document the options in the Xusage.txt file so that java will print them
  as part of its "java -X" help message.
- Document the options as part of the standard tool docs for the 'java' command.