Adds a public interface apm::process_install_xml to use install.xml
files subsequent to the bootstrap, change bootstrap to use the
provided api, adds install::xml namespace + functions to support the
various xml stanzas (such as set-parameter or set-join-policy) and a
clean extension mechanism via functions in the install::xml::action::
namespace. Thanks to Lee Denison for cleaning up and extending the
existing install functionality.
