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

#include "dbhelpers.h"
#include "includes.h"

/* Erase data */
void m_burn(void *data, unsigned int len) {

#if defined(HAVE_MEMSET_S)
	memset_s(data, len, 0x0, len);
#elif defined(HAVE_EXPLICIT_BZERO)
	explicit_bzero(data, len);
#else
	/* This must be volatile to avoid compiler optimisation */
	volatile void *p = data;
	memset((void*)p, 0x0, len);
#endif
}