signal: Keep only one list of emissions

There is no need to keep 2 lists.

This simplifies the code and gets rid of the only user inside glib of
G_HAVE_GROWING_STACK.

https://bugzilla.gnome.org/show_bug.cgi?id=736284
Bump version to 2.43.0

We have new API.
gfile: Clarify docs

Clarify corner cases that were unclear while reviewing a GTK patch.