This function works like ParamSpec.setQdata, but in addition,
a void (*destroy) (gpointer) function may be
specified which is called with data as argument when the pspec is
finalized, or the data is being overwritten by a call to
ParamSpec.setQdata with the same quark.
This function works like ParamSpec.setQdata, but in addition, a void (*destroy) (gpointer) function may be specified which is called with data as argument when the pspec is finalized, or the data is being overwritten by a call to ParamSpec.setQdata with the same quark.