By RICARDO CASTILLO     Here’s the sequence of events that led to a market selloff at the Mexican Stock Exchange (Bolsa Mexicana de Valores) that provoked the loss of nearly 6 percentage points and nearly 90 billion pesos over the last week, mostly for banks. First, on Wednesday, Nov. 7, came the not-so-casual news from the National Regeneration Movement (Morena) political party majority leader