The following scenes have been cut from some TV prints:
Bugs and Yosemite Sam play Russian Roulette.
Sam shoots Bugs's "jukeybox."
Source: The Censored Cartoons Page
See: this FAQ entry
Yes, it's included in the Looney Tunes Golden Collection, Volume One (2003) (V) Disc 1.
That's a pun joke, in which a "dark horse" has been elected as the "new mare". The term of "dark horse" refers to one who receives unexpected support as a candidate for the nomination in a political convention.
