pcbgit v0.7.4

Ready for a wider audience: protection against sign-up bots and render floods, and a smoother 3D view.

• Registration against bots, without a CAPTCHA: at most 3 new accounts per address an hour, a hidden honeypot field, and at most 50 accounts waiting for approval (registration pauses beyond that). Password hashing no longer blocks the server.
• Render queue per user: each owner's boards may have a limited number of renders waiting or running (10 by default, set under Admin → Instance → Limits and per user under Users; admins exempt). A push with more versions than that renders the newest; the rest can be rendered from the board's history.
• 3D view: panning (right drag) now runs as smoothly as rotating.

The database gains a column for the new per-user limit, added automatically at startup.