scripted-diff: Convert global Mutexes to GlobalMutexes

-BEGIN VERIFY SCRIPT-
sed -i -E -e '/^([a-z]+ )?Mutex [a-z]/ s/Mutex/GlobalMutex/' $(git grep -lE '^([a-z]+ )?Mutex [a-z]')
-END VERIFY SCRIPT-

src/rpc/blockchain.cpp

@@ -66,7 +66,7 @@ struct CUpdatedBlock
     int height;
 };
 
-static Mutex cs_blockchange;
+static GlobalMutex cs_blockchange;
 static std::condition_variable cond_blockchange;
 static CUpdatedBlock latestblock GUARDED_BY(cs_blockchange);