Error if both LEAmDNS and SimpleMDNS used

Author: earlephilhower

libraries/LEAmDNS/src/LEAmDNS.h

@@ -1348,3 +1348,8 @@ class MDNSResponder {
 }  // namespace esp8266
 
 #include <ESP8266mDNS.h>
+
+#define __LEAMDNS_H 1
+#ifdef __SIMPLEMDNS_H
+#error SimpleMDNS and LeaMDNS both included.  Only one allowed at a time.
+#endif

libraries/SimpleMDNS/src/SimpleMDNS.h

@@ -44,3 +44,8 @@ class SimpleMDNS {
 };
 
 extern SimpleMDNS MDNS;
+
+#define __SIMPLEMDNS_H 1
+#ifdef __LEAMDNS_H
+#error SimpleMDNS and LeaMDNS both included.  Only one allowed at a time.
+#endif