Copy constructor of Safelist shares state

[cschwier]

The copy constructor of Safelist public Safelist(Safelist copy) does not deep copy the data structures as advertised in the JavaDoc but shares the nested data structures, e.g. Map<TagName, Set<AttributeKey>>. This causes unexpected mutation.

An example would be:

Safelist safelist1 = Safelist.none().addAttributes("foo", "bar");
Safelist safelist2 = new Safelist(safelist1);
safelist1.addAttributes("foo", "baz");

final String html = "<foo bar=\"val\" baz=\"val\" />";
System.out.println(Jsoup.clean(html, safelist1));
System.out.println(Jsoup.clean(html, safelist2));

The second output should not contain the baz attribute but does.