Issue 87 in svnbook: ch06: mention 'htdigest' tool when mentioning digest auth

[svnbook at googlecode.com]

Comment #22 on issue 87 by cmpil... at gmail.com: ch06: mention 'htdigest'  
tool when mentioning digest auth
http://code.google.com/p/svnbook/issues/detail?id=87

Committed the screen-to-programlisting.diff patch in r3902, minus the last  
hunk which, technically, *was* screen output (a transcript of running 'cat'  
-- sneaky, sneaky, and a prime candidate for <example>-ification, by the  
way).  Thanks, again!