Initialize lcap and pwd to NULL. This allows a WARNS=6 clean build,

hence bump it to 6.

Note that the last commit message was not quite accurate.  While the
assumption exists in the code, it's not possible to have an
uninitialized p there because if lflag is set when username is NULL
then execution would be terminated earlier.

usr.sbin/jail/Makefile

@@ -5,6 +5,6 @@ MAN=	jail.8
 DPADD=	${LIBUTIL}
 LDADD=	-lutil
 
-WARNS?=	2
+WARNS?=	6
 
 .include <bsd.prog.mk>

usr.sbin/jail/jail.c

@@ -49,9 +49,9 @@ extern char	**environ;
 int
 main(int argc, char **argv)
 {
-	login_cap_t *lcap;
+	login_cap_t *lcap = NULL;
 	struct jail j;
-	struct passwd *pwd;
+	struct passwd *pwd = NULL;
 	struct in_addr in;
 	gid_t groups[NGROUPS];
 	int ch, i, iflag, lflag, ngroups, uflag, Uflag;