[RFA] PATCH to {extend,invoke,install,md}.texi for C++ attributes and typos

[Jeffrey A Law]

  In message <flelytx2su.fsf@sel.cmla.ens-cachan.fr>you write:
  >   In Standard C++, objects defined at namespace scope are guaranteed
  >   to be initialized in an order in strict accordance with that of their
  >   definitions @emph{in a given translation unit}.  No guarantee is
  >   made for initializations accross translation units.  However, GNU
  >   C++ allows users to control the order of initialization of objects
  >   defined at namespace socpe with the @code{init_priority} attribute by 
  >   specifying a relative @var{priority}, a constant integral expression(?). 
Seems reasonable to me.
jeff