class autotools: add function 'autotools_stage_all' that automatically stages

class autotools: add function 'autotools_stage_all' that automatically stages
include files and libraries for packages that obey DESTDIR. This can be used to
remove a lot of duplicated metadata in do_stage() of packages that inherit autotools.
Note that you need to call autotools_stage_all manually in do_stage. It may be
added to do_stage() eventually, but for now we want to do the transition step-by-step.
Feel free to convert do_stage of autotools packages to using autotools_stage_all.