early directory validation

Allow early prefix directory validation to help prevent
failed games and lost save files due to incorrect config
file settings.

sys/share/pcmain.c

@@ -105,6 +105,9 @@ char *argv[];
 
 	register int fd;
 	register char *dir;
+#ifdef NOCWD_ASSUMPTIONS
+	char failbuf[BUFSZ];
+#endif
 
 #if defined(__BORLANDC__) && !defined(_WIN32)
 	startup();
@@ -171,6 +174,14 @@ char *argv[];
 #endif
 	initoptions();
 
+#ifdef NOCWD_ASSUMPTIONS
+	if (!validate_prefix_locations(failbuf)) {
+		raw_printf("Some invalid directory locations were specified:\n\t%s\n",
+				failbuf);
+		 nethack_exit(EXIT_FAILURE);
+	}
+#endif
+
 #if defined(TOS) && defined(TEXTCOLOR)
 	if (iflags.BIOS && iflags.use_color)
 		set_colors();