Variation of JavaScriptHeaderContributor: ExternalJavaScriptHeaderContributor

Where JavaScriptHeaderContributor contributes a reference to a javascript file relative to the context, ExternalJavaScriptHeaderContributor allows references to any javascript files just as long as the reference is recognized by the 'src' attribute of the <script> element.
This is not really an extension, rather a 'down'tesnsion since ExternalJavaScriptHeaderContributor equals (JavaScriptHeaderContributor - the lines of code that prepend the getContextPath to the given reference).

mf