Autoindex: escape '?' in file names.

Autoindex: escape '?' in file names.

For files with '?' in their names autoindex generated links with '?' not
escaped.  This resulted in effectively truncated links as '?' indicates
query string start.

This is an updated version of the patch originally posted at [1].  It
introduces generic NGX_ESCAPE_URI_COMPONENT which escapes everything but
unreserved characters as per RFC 3986.  This approach also renders unneeded
special colon processing (as colon is percent-encoded now), it's dropped
accordingly.

[1] http://nginx.org/pipermail/nginx-devel/2010-February/000112.html

Reported by Konstantin Leonov.