Bug 945572 part 1.  Make NS_NewHTMLElement take an Element** outparam instead of an nsIContent** one.  r=smaug
Bug 945572 part 2.  Make NS_NewXULElement take an Element** outparam instead of an nsIContent** one.  r=smaug
Bug 945572 part 3.  Make NS_NewMathMLElement take an Element** outparam instead of an nsIContent** one.  r=smaug
Bug 945572 part 4.  Make NS_NewXMLElement take an Element** outparam instead of an nsIContent** one.  r=smaug
Bug 945572 part 5.  Make NS_NewSVGElement take an Element** outparam instead of an nsIContent** one.  r=smaug
Bug 945572 part 6.  Make NS_NewElement take an Element** outparam instead of an nsIContent** one.  r=smaug
Bug 945573.  Make nsITextControlElement::GetPlaceholderNode return Element*.  r=smaug