Fix int overflow on 32-bit architectures

[Arnie97]

$  GOARCH=386 GOOS=linux go build ./...
# github.com/dolthub/dolt/go/store/skip
store/skip/list.go:152:21: maxCount (untyped int constant 4294967294) overflows int

See also dolthub/vitess#216

[timsehn]

Thanks @reltuk will look at this one.

[reltuk]

I think this might be better as:

Suggested change

	maxCount = math.MaxInt - 1
	maxCount = math.MaxInt32 - 1

for now. The structure will not work with a number of entries > MaxUint32, so we don't want to set it to MaxInt - 1 on a 64-bit platform.

For now we can give up the two billion possible extra entries on 64-bit in order to get this working on 32-bit.

[reltuk]

Thank you for the report! Generally looks great to me. One suggested change.