[NbtkExpander] Use a floating point value in the parameter to g_object_new
[NbtkExpander] Use a floating point value in the parameter to g_object_new

When creating the NbtkButton the "x-align" parameter is a float not an
integer. Not using the correct type for the value here in the vaargs function
causes data corruption.

jonnylamb/mx,clutter-project/mx,pwithnall/mx,clutter-project/mx,pwithnall/mx,pwithnall/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx