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

0 files changed, 0 insertions, 0 deletions