web/.htaccess: auto-detect dotpath in query string: also auto-detect dotpath for query strings appended to a username-based prefix, so that these don't need to have . prepended to make them appendable

web/username_prefix.php: no prefix: use $_SERVER["SCRIPT_URL"] instead of rtrimming $_SERVER["REQUEST_URI"]

web/username_prefix.php: has prefix: use same expr whether or not it has a query string, because the with-query-string expr works for both cases

web/username_prefix.php: use if statements instead of `? :` for clarity

web/username_prefix.php: use $subpath instead of $_SERVER["PHP_AUTH_USER"] for clarity

web/.htaccess, username_prefix.php: username-based prefix subpaths: support dotpath in query string (which will be appended verbatim to the prefix). use "__?@__" instead of "__?__&" to signal username-based prefix, so that the query string does not end in a dangling & .

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