The :opacity property is defined using a GParamSpecUchar. This usually
leads to issues with language bindings that don't have an 'unsigned
char' type and that need to explicitly handle the conversion between
G_TYPE_UCHAR and G_TYPE_INT or G_TYPE_UINT.
The property definition already specifies an interval size of [0, 255]
on the values; more importantly, GObject already implicitly transforms
between G_TYPE_UCHAR and G_TYPE_UINT (the GValue transformation
functions are registered at type system initialization time) so
switching between a GParamSpecUchar and a GParamSpecUint should not be
an ABI break.
I have tested a simple program using the opacity property before and
after the change and I cannot see any run-time warnings related to this
issue.
