r1699, r1700, r1701, r1702, r1707 merge:

r1699, r1700, r1701, r1702, r1707 merge:

upstream parse_header fix and optimization,
fix fastcgi_catch_stderr segfault merged in r1524:

*) return NGX_HTTP_UPSTREAM_INVALID_HEADER for invalid status
*) return NGX_ERROR instead of NGX_HTTP_INTERNAL_SERVER_ERROR
   in u->parse_header()
*) return NGX_HTTP_UPSTREAM_INVALID_HEADER instead of NGX_HTTP_BAD_GATEWAY
   to go to a next upstream on invalid_header condition
*) now ngx_conf_set_str_array_slot() tests NGX_CONF_UNSET_PTR
   this fixes fastcgi_catch_stderr segfault
*) ngx_http_upstream_hide_headers_hash()
*) proxy/fastcgi pass_header/hide_header use
   ngx_http_upstream_hide_headers_hash()