`Equal()` panics when called with bitsets with different `set` lengths

[omerfirmak]

bitset/bitset.go

Lines 603 to 615 in 312c8c2

	if b.length != c.length {
	return false
	}
	if b.length == 0 { // if they have both length == 0, then could have nil set
	return true
	}
	// testing for equality shoud not transform the bitset (no call to safeSet)
	for p, v := range b.set {
	if c.set[p] != v {
	return false
	}
	}

even tho b.length == c.length, len(b.set) and len(c.set) could be different.

Equal should check if wordsNeeded(b.length) number of words are equal.

[lemire]

I agree.