BigInt @safe https://issues.dlang.org/show_bug.cgi?id=13607

Another try: https://issues.dlang.org/show_bug.cgi?id=13607
This is just a nitpick, but for single line if/else clauses, there's really no need to insert extra braces for them. I'd also take the opportunity to break the if-clause into two lines, though, something like this:
````
if (sofar == 0)
    data = ZERO;
else
    data = trustedAssumeUnique(tmp[0 .. sofar]);
````
Oh, and it would be nice to add spaces around the `..`.

All non-blockers, but little readability improvements to Phobos code.