`gimp_unit_store_get_value()` clashes with the `get_value()` method of
its parent class GtkTreeStore. This means trouble for bindings, as seen
here in some pseudocode:
```vala
var unit_store = new Gimp.UnitStore();
// Which function are we referencing here, the one from GtkTreeStore or
// the one from GimpUnitStore? Worse, they both have different arguments
unit_store.get_value( ... )
```
The GIR parser is giving warnings because both e.g. a signal, a
corresponding vfunc and a method emitting it are named
"channel_changed", which can and will give issues in some bindings.
The easiest option is to follow the general convention of starting the
signal emitters with `emit_`, which also makes clear the intention of
the method.
Right now, we get the following warnings when building the docs:
> gtk-doc.xsl: For acronym (nullable) no value found
This is because we're not adding the generated annotation glossary to
the docs sgml (presumably because we didn't need it as we didn't use
GObject-Introspection yet). This commit adds those lines and thus fixes
the warnings.
GimpSpinButton is a drop-in replacement for (and a subclass of)
GtkSpinButton. Unlike GtkSpinButton, it avoids updating the
adjustment value when losing focus, unless the entry text has
changed. This prevents accidental loss of precision, when the
adjustment value can't be accurately displayed in the entry.
GimpBusyBox is used to show a message indicating an operation is in
progress. It's basically just a spinner and a label, with some
styling.
We're going to use it both in app/ and in a plug-in.
Its API was too limited, and adding parameters for what we need next
would be equally random. It's a rarely used and mostly internal
widget, so simply use g_object_new().
because it confuses gtk-doc and breaks some links. Also change the
"Index of new symbols in GIMP 2.x" sections to be what seems to be the
modern standard (looked at the GLib and GTK+ docs), and update some
other stuff.
