v0.12.0: Alpha release #3

This is the third Alpha release, issued as a follow-up to the previous Alpha
releases. It contains a number of minor improvements.

Changes:

• A new "--ignore-unstarted" option to dinitctl, causing it to return success when attempting to restart a service which is not started (including when no service description for it exists).
• Add an "always-chain" service option, so that chaining to another service (as specified via the "chain-to" setting) becomes unconditional.
  Feature contributed by Alexander Sherikov.
• Add support for multiple service directories to be specified (via multiple --services-dir options).
  Feature contributed by Alexander Sherikov.
• Improve control socket creation / stale socket removal. Previously, a system instance would unconditionally unlink a pre-existing socket file, and non-system instances would fail if a pre-existing socket file existed (even if it was not active, i.e. no dinit instance was accepting connections on it). Now, if there is an existing socket file, dinit will attempt to connect to it, and will refuse to start if this succeeds, or unlink it otherwise. Unfortunately this cannot be done atomically, so it should not be relied on as a general means to prevent more than one instance of dinit from starting.