beam_dead: Optimize branches from relational conditionals

The BEAM compiler translates code such as:

  is_hex_digit(D) when $0 =< D, D =< $9 -> true;
  is_hex_digit(D) when $a =< D, D =< $z -> true;
  is_hex_digit(D) when $A =< D, D =< $Z -> true;
  is_hex_digit(_) -> false.

to something like this:

    L0: test is_ge L1 {x,0} 48
        test is_ge L1 57 {x,0}
        move true {x,0}
        return.

    L1: test is_ge L2 {x,0} 97
        test is_ge L2 122 {x,0}
        move true {x,0}
        return

    L2: test is_ge L3 {x,0} 65
        test is_ge L3 90 {x,0}
        move true {x,0}
        return

    L3: move false {x,0}
        return

We can see that tests will be repeated even if they cannot possibly
succeed. For instance, if we pass in {x,0} equal to 32, the first
test that {x,0} is greater than or equal to 48 at L0 will fail.
The control will transfer to L1, where it will be tested whether
{x,0} is greater than 97. That test will fail and control
will pass to L2, where again the test will fail.

The compiler can do better by short-circuiting repeating tests:

    L0: test is_ge L3 {x,0} 48
        test is_ge L1 57 {x,0}
        move true {x,0}
        return.

    L1: test is_ge L2 {x,0} 97
        test is_ge L3 122 {x,0}
        move true {x,0}
        return

    L2: test is_ge L3 {x,0} 65
        test is_ge L3 90 {x,0}
        move true {x,0}
        return

    L3: move false {x,0}
        return

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