sh: Read .profile from the home directory (or / if HOME is not set).

In most cases, login shells are started from the home directory, but not in
all, such as xterm -ls.

This commit depends on r222957 for read_profile() performing parameter
expansion.

PR:		bin/50569

bin/sh/main.c

@@ -150,7 +150,7 @@ main(int argc, char *argv[])
 state1:
 		state = 2;
 		if (privileged == 0)
-			read_profile(".profile");
+			read_profile("${HOME-}/.profile");
 		else
 			read_profile("/etc/suid_profile");
 	}