PIVOT-1012, PIVOT-999:  Many more places can use the "Utils" methods
to do parameter validation.  Use the "forEach" method with a bunch of
ListenerList implementations.

Code cleanup:  Add a "checkSkin" method in Component that does
the common check to make sure the skin being installed implements
the correct interface for the component.

Update all the places that were doing this check to use this new
method.

Some local variable renaming.

Add some message text to some exceptions that previously had none.

Add a new "setRange" method to Slider using the "Span(Sequence<?>)"
constructor.  Add Javadoc to that constructor.

Reflow some comments that had been wrapped weirdly.


git-svn-id: https://svn.apache.org/repos/asf/pivot/trunk@1819096 13f79535-47bb-0310-9956-ffa450edef68
35 files changed