The NGX_PTR_SIZE macro is only needed in preprocessor directives where
it's not possible to use sizeof().

The directive already works inside stream upstream blocks.

The code failed to ensure that "s" is within the buffer passed for
parsing when checking for "ms", and this resulted in unexpected errors when
parsing non-null-terminated strings with trailing "m".  The bug manifested
itself when the expires directive was used with variables.

Found by Roman Arutyunyan.

The option disables sending hostname in the syslog message header.  This is
useful with syslog daemons that do not expect it (tickets #677 and #783).

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

This change fixes the "comparison between signed and unsigned integer
expressions" warning, introduced in 5e6142609e48 (1.9.4).