I've just realised that there was a lurking gotcha in the naming of

I've just realised that there was a lurking gotcha in the naming of
HTML files after the pathnames they represent: in recursive -H mode
(dumping a full set of HTML reports into the filesystem), there could
be a name clash between index.html representing the top level, and
index.html representing a subdirectory called 'index'.

Fix by detecting the clash and adding gratuitous escaping in the
latter case; this is not a fully general solution that will work with
any list of string formats, but it should be good enough for the
current set.

git-svn-id: svn://svn.tartarus.org/sgt/agedu@9417 cda61777-01e9-0310-a592-d414129be87e