man: use same header for all files

man: use same header for all files

The "include" files had type "book" for some raeason. I don't think this
is meaningful. Let's just use the same everywhere.

$ perl -i -0pe 's^..DOCTYPE (book|refentry) PUBLIC "-//OASIS//DTD DocBook XML V4.[25]//EN"\s+"http^<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"\n  "http^gms' man/*.xml