Simplify list_foreach iteration

[Jiri Svoboda]

Currently list_foreach presents a link_t * as an iterator. This leads to almost any list_foreach loop over a list of foo_t to look like this:

list_foreach(list, link) {
    foo_t *foo = list_get_instance(link, foo_t, link_field);
    ... use foo ...
}

therefore it would make sense to simplify the syntax to either:

list_foreach(list, foo_t, foo, link_field) {
   ... use foo ...
}

or

list_foreach(list, link_field, foo_t, foo) {
   ... use foo ...
}

the only downside being, one has to remember the correct order of four arguments.

Please let me know your comments on this proposal.

[Jiri Svoboda]

Implemented in mainline,1946 (the latter variant).