NEW YORK (Reuters) - Morgan Stanley Smith Barney, one of the three lead underwriters on the Facebook Inc IPO, has increased the number of Facebook shares it will allow advisers to allocate to each client account. The firm previously set a cap of 500 shares per retail client, but e-mailed advisers late on Thursday afternoon that it had increased the limit to 5,000 shares, according to two sources familiar with the situation, who declined to be named because they are not permitted to speak to the press. ...