nnrpd/article.c: GetHeader() and continuation header lines

[jani+inn at ifi.uio.no]

I've come across a minor problem that's in 2.3.1, CURRENT and STABLE.

If a header line is broken up into several continued lines, as
e.g. Subject, Newsgroups and References may be, GetHeader() doesn't
cope with it.

This may cause problems e.g. with PERMartok() in nnrpd/misc.c and
Python authorization modules, or as the case is for me, with a small,
personal statistics patch for CMDfetch in nnrpd/article.c.