stylable: Don't force a style-changed emission when setting style
stylable: Don't force a style-changed emission when setting style

The style-changed signal prototype used to include the old style, but this
has changed to be flags associated with the emission.

Fix mx_stylable_set_style so that it doesn't end up forcing a recursive
style-changed emission, and fix the documentation for the signal itself.

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