Eliminate some entity copies in lathe groups.

[phkahler]

Eliminates a crash due to copy numbers going over 1000.
May break some older files with constraints on lathed entities.

[phkahler]

Oops. This also has changes from #581

[phkahler]

Rebased.

[whitequark]

Thanks for the fix!

Can I ask you to format the git commits a bit differently? The usual convention is to put the summary on the first line, then a blank line, then a detailed description below. This makes commit messages much easier to read in tools like gitk, e.g. here's how this commit this commit looks there:

and here's how your previous one looks (I took the liberty of reformatting it while merging):

(They'll also be a bit easier to read on GitHub as well, though the difference is much smaller there.)

[phkahler]

No problem. When I put a single line comment in the commit. When I created a PR it looked bad on github so I edited there. Probably best to leave it alone.

[whitequark]

Oh yeah, I agree it's pretty annoying that commit messages look best with manual wrapping if you're viewing them in gitk, but the very same commit messages look a lot worse on GitHub when it automatically copies them into the PR body. I expect a lot more people to read git history than pull request comments so I spend effort to make the history readable. Sometimes I edit things in the PR body to make them look nicer but that's only if a lot of people will be potentially looking at it.