Move helper scripts to build-aux.

* compile, config.guess, config.rpath, config.sub, depcomp, ltmain.sh
* doc/mdate-sh, doc/texinfo.tex, install-sh, missing: Move to
build-aux/.
* Makefile.am (EXTRA_DIST): Remove config.rpath - it is implicitly
distributed.
* configure.ac (AC_CONFIG_AUX_DIR): New.
(AM_SILENT_RULES): New.
Use the generic autogen.sh script.

* autogen.rc: New.
* Makefile.am (EXTRA_DIST): Add it.
* autogen.sh: Update from GnuPG.