Switch to camlistore/lock

[cznic]

https://github.com/camlistore/lock

It's better:

• Selects approach per platforrm.
• Handles stale lock files.

[cznic]

Now blocked on 0.

[tgulacsi]

Issued pull request camlistore/lock#2 for windows support - hope this will be usable.

[cznic]

Thanks! Hope Brad accepts the PR soon.