fix: web/index.php: directory index: don't append QUERY_STRING, as this is not used by /all

web/.htaccess: username-based prefix subpaths: removed usernames_disabled env var because the bug that appeared to require this has now been fixed

bugfix: web/.htaccess: username-based prefix subpaths: also need to check original URL (REDIRECT_REQUEST_URI), in addition to current URL (REQUEST_URI) to see if usernames should be disabled

web/.htaccess: username-based prefix subpaths: allow explicitly disabling in a RewriteRule to handle special cases

web/.htaccess: auto-detect dotpath: removed handling of no longer used @ prefix (used to be used by username-based prefix subpaths)

bugfix: web/index.php: directory index: use QUERY_STRING, not HTTP_AUTHORIZATION (HTTP_AUTHORIZATION was probably left over from a previous attempt to provide username-based prefix subpaths)

web/.htaccess, username_prefix.php: username-based prefix subpaths: don't require the // at the end , to avoid clutter. IMPORTANT: in order to access the home page after visiting a URL with a username, you must now append "." to the host ("vegpath.org.") (other pages are not affected by this problem). since vegpath.org is a URL shortener, this is a worthwhile tradeoff to avoid needing the // suffixes everywhere.

bugfix: web/.htaccess: subdomains: each path element must be non-empty, to avoid matching a trailing . incorrectly

web/.htaccess: username-based prefix subpaths: updated documentation to use leading // instead of trailing ? or ?@

web/username_prefix.php: $_SERVER["PHP_AUTH_USER"] test: factored $_SERVER["SCRIPT_URL"] out of both branches of if statement