merge

prepare support for a 'context toolbar', used in tracker but will much probably be backported in default primary view. Turn pdfview component into a toolbar element

missing space between label and value

[web] safety belt to avoid overriding pageid with loadxhtml() HtmlHeaders.define_var() now accepts a third optional 'override' paramater. If set to False, the variable won't be evaluated if it's already defined in the page.