[Twisted-Python] INCOMPATIBLE CHANGE: Removal of t.c.ssh.filetransfer.FileTransferClient.wasAFile

[Wim Lewis]

In PR 949 ("Remove “terrible hack” in t.c.ssh.filetransfer.FileTransferClient", trac bug 9362) I'm removing an attribute of FileTransferClient which I'm pretty sure was never intended to be public. Adi Roiban points out that this is technically a compatibility-breaking change, though, and so it needs more public review.

My reasoning for thinking that this will not break any user code: the attribute, although not prefixed with an underscore, was undocumented; anyone relying on it would have had to read the source code to discover what it does, and in the source it was commented as a "TERRIBLE HACK". I'd hope this would be enough of a warning. (Also, I can't think of a use for it.)

trac: https://twistedmatrix.com/trac/ticket/9362
pr: https://github.com/twisted/twisted/pull/949