Make a web folder accessible. This assumes listings are provided in html form by requesting links ending in a slash. For example, http://autoplot.org/data/pngwalk/. Links to resources "outside" of the filesystem are not considered part of the filesystem. Again, this assumes listings are HTML content, and I suspect this will be changing (xml+client-side-xslt)...
Create a filesystem from the URI. Note "user@" will be added to the URI if credentials are needed and added automatically.
dumb method looks for / in parent directory's listing. Since we have to list the parent, then IOException can be thrown.
return true if the regular expression for the file is actually a single file with no wildcards. This is tricky because for years a single period (".") has been left in the name, so that "." matches ".", and really screen.png would match screen_png. To contain this logic, this routine is introduced. Presently it just checks for "screen.png" so that a pngwalk of each screenshot (https://autoplot.org/jnlp/v$x/screen.png) can be made, which is useful when looking for old versions.
list the directory, using the cached entry from listDirectoryFromMemory, or by HtmlUtil.getDirectoryListing. If there is a ro_cache, then add extra entries from here as well. Note the following extentions are hidden: .css, .php, .jnlp, .part.
HTTP listings are really done by querying the single file, so support this by issuing a head request