Please review a moderately simple change to have the standard doclet
better support repeated instances of {@systemProperty} and {@index} in a
single file.
The problem is that each use for a given name creates a new instance of
an id for that name, leading to duplicate definitions for the id. The
fix is to make the occurrences unique by appending a suffix to the ids
so that the ids become unique.
Although the bug was encountered with repeated `{@systemProperty}`, the
fix addresses repeated `{@index}` as well.
-- Jon
JBS: https://bugs.openjdk.java.net/browse/JDK-8225321
Webrev: http://cr.openjdk.java.net/~jjg/8225321/webrev.00/
