devel/got: update to 0.64

User-visible changes:

• make 'got rebase' switch the work tree if no commits need rebasing
• let gotadmin find the repository automatically if invoked in a work tree
• preserve binary files during updates and merges instead of leaving them empty
• allow sorting references by timestamp in tog ref view
• add got ref -t option to sort listed references by modification time
• add got branch -t option to sort listed branches by modification time