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

--- a/scpmisc.c	Wed Mar 20 15:03:40 2019 +0100
+++ b/scpmisc.c	Wed Mar 20 15:09:19 2019 +0100
@@ -102,7 +102,7 @@
 
 	len = strlen(str) + 1;
 	cp = xmalloc(len);
-	strncpy(cp, str, len);
+	strlcpy(cp, str, len);
 	return cp;
 }