Add tools/openbsd to distribution package.
* include/Makefile.am: include files should have been installed
under sane/ directory when converted to automake.
* doc/Makefile.am: Cleanup. Use automake's built in support to
install docs within subdirectories.
doc/Makefile to use automake. Main difference is that
no longer installs man pages for backends that are not
compiled. Moved install ownership of $top_srcdir docs
to $top_srcdir's Makefile.