Add md5 testing to netplay

Allows to test current game, an arbitrary game or the sdcard of all players
at once.

Source/Core/Core/NetPlayProto.h

@@ -58,6 +58,12 @@ enum
   NP_MSG_TIMEBASE = 0xB0,
   NP_MSG_DESYNC_DETECTED = 0xB1,
 
+  NP_MSG_COMPUTE_MD5 = 0xC0,
+  NP_MSG_MD5_PROGRESS = 0xC1,
+  NP_MSG_MD5_RESULT = 0xC2,
+  NP_MSG_MD5_ABORT = 0xC3,
+  NP_MSG_MD5_ERROR = 0xC4,
+
   NP_MSG_READY = 0xD0,
   NP_MSG_NOT_READY = 0xD1,