rebase: always pass destination as revnum to _handleskippingobsolete() We were passing it as a revision number in one place and as a context in another. It worked because the only use was in "repo[dest].rev()", but it was confusing. By always passing a revision number, we can also remove that unnecessary lookup.

patch: remove unused fsbackend._join() The function lost its last caller in 2a095d3442e0 (patch: replace functions in fsbackend to use vfs, 2014-06-05) when the callers started relying on the opener to do the join.

patch: add close() to abstractbackend patchbackend() seems to call it on an arbitrary backend, so it seems to be part of the API. Since all subclasses do something in their close() methods, I decided to let this one raise an exception rather than just pass.