Heimdal isn't really supported right now. Say so, and offer a possibility

to force the use of Heimdal, and warn if that's used.
PR: 346

Configure

@@ -994,6 +994,17 @@ else
 	my ($lresolv, $lpath, $lext);
 	if ($withargs{"krb5-flavor"} =~ /^[Hh]eimdal$/)
 		{
+		die "Sorry, Heimdal is currently not supported\n";
+		}
+	##### HACK to force use of Heimdal.
+	##### WARNING: Since we don't really have adequate support for Heimdal,
+	#####          using this will break the build.  You'll have to make
+	#####          changes to the source, and if you do, please send
+	#####          patches to openssl-dev@openssl.org
+	if ($withargs{"krb5-flavor"} =~ /^force-[Hh]eimdal$/)
+		{
+		warn "Heimdal isn't really supported.  Your build WILL break\n";
+		warn "If you fix the problems, please send a patch to openssl-dev@openssl.org\n";
 		$withargs{"krb5-dir"} = "/usr/heimdal"
 			if $withargs{"krb5-dir"} eq "";
 		$withargs{"krb5-lib"} = "-L".$withargs{"krb5-dir"}.