Catholic Papal infallibility doctrine:
The Pope cannot err 'when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he defines a doctrine concerning faith or morals to be held by the whole Church'" (First Vatican Council, "First Dogmatic Constitution on the Church", chapter 4, 9)
Mormon president infallibility doctrine after Joseph Smith:
"The Lord will never permit me or any other man who stands as President of this Church to lead you astray. It is not in the programme." (Wilford Woodruff, General Conference, October 6, 1890)
It appears that the new Mormon infallibility doctrine is more comprehensive than Catholic infallibility, since Pope's are only infallible when defining doctrine or morals.
"Among the vast number of the Keys of the Kingdom of God Joseph presented the following one to the Twelve for there benefit in there experience & travels in the flesh which is as follows. In order to detect the devel when he transforms himself nigh unto an angel of light..." (Wilford Woodruff, Journal. June 27, 1839)