Previous interface of ngx_open_dir() assumed that passed directory name
has a room for NGX_DIR_MASK at the end (NGX_DIR_MASK_LEN bytes).  While all
direct users of ngx_dir_open() followed this interface, this also implied
similar requirements for indirect uses - in particular, via ngx_walk_tree().

Currently none of ngx_walk_tree() uses provides appropriate space, and
fixing this does not look like a right way to go.  Instead, ngx_dir_open()
interface was changed to not require any additional space and use
appropriate allocations instead.

The bgcolor attribute overrides compatibility settings in browsers
and leads to undesirable behavior when the default font color is set
to white in the browser, since font-color is not also overridden.

No functional changes.

This fixes content type set in stub_status and autoindex responses
to be usable in content type checks made by filter modules, such
as charset and sub filters.

This allows to build a directory listing whenever a loop exists in symbolic
link resolution of the path argument.

This prevents ngx_http_finalize_request() from issuing
ngx_http_special_response_handler() on a freed context.