Add target to build `info' file.

We probably already require a new enough version of Halibut that this isn't
a problem; nevertheless, I've put it in a separate target for now.

[originally from svn r5595]

doc/blurb.but

@@ -12,9 +12,12 @@ page</a>.</p>}
 
 \cfg{html-template-fragment}{%k}{%b}
 
+\cfg{info-max-file-size}{0}
+
 \cfg{xhtml-contents-filename}{index.html}
 \cfg{text-filename}{puttydoc.txt}
 \cfg{winhelp-filename}{putty.hlp}
+\cfg{info-filename}{putty.info}
 
 PuTTY is a free (MIT-licensed) Win32 Telnet and SSH client. This
 manual documents PuTTY, and its companion utilities PSCP, PSFTP,