bugfix: web/.htaccess: auto-detect dotpath in query string: don't exclude dotpaths that come before a normal query string (&k=v...)

web/.htaccess: auto-detect dotpath in query string: documented what each RewriteCond does

web/.htaccess: auto-detect dotpath in query string: use %{QUERY_STRING} instead of %0 for clarity

web/.htaccess, web/username_prefix.php: username-based prefix subpaths: support query strings in addition to paths

web/index.php: removed no longer needed redirection of username-based prefix subpaths, which is now handled by web/.htaccess

web/.htaccess: handle username-based prefix subpaths (of the form "subpath@url?") for all paths rather than just for the root (which were handled by index.php)

added web/username_prefix.php, for use with username-based prefix redirects

web/index.php: subpath@host? redirects: also support multiple @ and nested . in prefix: a@b.c@host? -> host?b.c.a

web/index.php: support prefix redirect of the form subpath@host? , which is better than subpath.host because case is preserved and special chars allowed. (must require trailing ? for redirect, to avoid needing login to view the page itself.)

bugfix: web/index.php: full directory index: appending query string: need to use $_SERVER["QUERY_STRING"], not $_SERVER["HTTP_AUTHORIZATION"] for this