Revamp config/build to keep generated files out of CVS (some libtool files

Revamp config/build to keep generated files out of CVS (some libtool files
were out of date, and we've previously seen expat.h out of sync).

*) Use new script "buildconf.sh" to create the set of generated files
   (aclocal.m4, config.h.in, configure). This is intended to be used by
   developers (rerun when configure.in changes) and just before a release
   (releases include these outputs).

   Developers now need the "autoconf" and "libtool" packages.

*) config.h.in is now built by autoheader and includes bits from acconfig.h
   rather than manual construction/maintenance. (renamed from config.hin)

*) added conftools/PrintPath from the ASF; it is a portable "which"

*) added "extraclean" target to top-level Makefile to get rid of all
   generated files (return to pure CVS state; before buildconf.sh)

*) updates various bits for config.hin -> config.h.in rename

*) no longer need to delete the ".deps" subdir since we don't create it
   anymore (dependencies are explicit rather than auto-generated).