perlPackages: add SGMLSpm

Required by iputils to create the manpages.
Adding the sgml dtd for docbook 3.1

Required by iputils manpages.
Adding setup-hook for opensp, to set the sgml catalog files

This sets the SGML_CATALOG_FILES, similar to how libxml2 does the same with
XML_CATALOG_FILES.

I based the hook on the libxml2 one, and I followed the instructions about this
variable here:
http://docbook.sourceforge.net/release/dsssl/1.79/doc/install.html
iputils: build and install the manpages