Filter interface should declare negate(), and() and or().

[rolfl]

Currently the and(), negate() and or() methods are defined on the AbstractFilter class only. Since these methods are not on the Filter interface, it makes it hard to access them. The not-so-obvious example of an issue is that it is not possible to do things like build a Filter that selects all elements except those with the name 'notthis' and 'notme'. It would be logical to have the structure:

ElementFilter notme = new ElementFilter("notme");
ElementFilter notthis = new ElementFilter("notthis");

Filter orfilter = notme.or(notthis);
Filter neitherfilter = orfilter.negate();

[rolfl]

fixed by commit 3217942