use strlcpy & strlcat (#74) * refactor checkpubkeyperms() with safe BSD functions fix gcc8 warnings ``` svr-authpubkey.c: In function 'checkpubkeyperms': svr-authpubkey.c:427:2: warning: 'strncat' specified bound 5 equals source length [-Wstringop-overflow=] strncat(filename, "/.ssh", 5); /* strlen("/.ssh") == 5 */ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ svr-authpubkey.c:433:2: warning: 'strncat' specified bound 16 equals source length [-Wstringop-overflow=] strncat(filename, "/authorized_keys", 16); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ``` see https://www.sudo.ws/todd/papers/strlcpy.html * restore strlcpy in xstrdup see original https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/xmalloc.c?rev=1.16

#ifndef DROPBEAR_OPTIONS_H
#define DROPBEAR_OPTIONS_H

/* 
            > > > Don't edit this file any more! < < <
            
Local compile-time configuration should be defined in localoptions.h
in the build directory.
See default_options.h.in for a description of the available options.
*/

/* Some configuration options or checks depend on system config */
#include "config.h"

#ifdef LOCALOPTIONS_H_EXISTS
#include "localoptions.h"
#endif

/* default_options.h is processed to add #ifndef guards */
#include "default_options_guard.h"

/* Some other defines that mostly should be left alone are defined
 * in sysoptions.h */
#include "sysoptions.h"

#endif /* DROPBEAR_OPTIONS_H */