Split autogen.sh into autopull.sh and autogen.sh.

* autopull.sh: New file, based on autogen.sh.
* autogen.sh: Remove code that was moved to autopull.sh. Remove
--skip-gnulib option.
* Makefile.devel (all): Remove srclib/Makefile.gnulib.
* Makefile.in (SOURCE_FILES): Add autogen.sh.
* HACKING: Mention autopull.sh.
11 files changed