Fix a segfault in lash, hush, and cmdedit. Each of these used

xgetcwd, but did not check the return for a NULL, and then continued
to call strlen on the NULL when the cwd had been removed from under it.
 -Erik

libbb/messages.c

@@ -58,4 +58,7 @@
 #ifdef L_name_longer_than_foo
 	const char * const name_longer_than_foo = "Names longer than %d chars not supported.";
 #endif
+#ifdef L_unknown
+	const char * const unknown = "(unknown)";
+#endif