Here's a snippet from my machine changelogs. I needed libxml in slink, but it isn't a package, so I retrieved the sources from unstable and built them. At the end I discovered:

     I had to create a symbolic link by hand in /usr/include
	ln -s libxml2/libxml libxml
     (e.g. /usr/include/libxml points to /usr/include/libxml2/libxml)
     I think this directory structure is a bug in the package.