genlist: Fix more tree issues (expanded state)

genlist: Fix more tree issues (expanded state)

This fixes a lot of cases where a genlist node (of any type)
with children may have appeared in the invalid expanded or
contracted state.

Before this patch, the test case "Genlist tree, Relative insert"
looked like below (all items are programmatically added):

> A
  > 1
  > 2
> B
  > 3
  > 4

The problem above is that A and B have visible children but
still believe they are in contracted state. This patch ensures
that A and B will be marked as expanded, but will do so without
firing an "expanded" signal and definitely without the
"expand,request" signal.

After this patch, the test case will look like this:

v A
  > 1
  > 2
v B
  > 3
  > 4

Which is more correct. Note that this test case does not handle
any expand/contract signal.

NOTE: This is a behaviour break!