* configure.in: new checking for dot and doxygen.
* template/Doxyfile.template: merged with Doxyfile.in.
configured some options.
* common.mk (capi): use $(DOXYGEN) instead of "doxygen".
(Doxyfile): removed a duplicate entry in the dependency.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@23895 b2dd03c8-39d4-4d8f-98ff-823fe69b080e