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

[svnbook at googlecode.com]

Comment #21 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

By the way, I don't recall adding any <example>'s recently.  As you can see  
near the bottom of http://svnbook.red-bean.com/en/1.0/, the examples from  
Chapter 6 have been around since the book's beginning.  To be clear, I'm  
*not* saying we should caption every example -- it's just that there are  
some (such as the ones already so captioned) which make for useful  
quick-references for folks not looking to read the whole chapter.