Fix install permissions, errors and, or omissions

On some/most  unix systems the packager should not be 'root' and, or one should not build and install a package as superuser; hence executing 'ldconfig' is not possible for a regular user or packager.

I have added a missing "mkdir -p $(DESTDIR)$(libdir)" and a target "distclean", the later is required by some package build systems e.g. both of Debian the package build frameworks.