Fail better if .profile file can't be modified

[brson]

Installation will fail if ~/.profile can't be modified. This may or not be the right thing to do, but it should fail gracefully, not with the default I/O error.

[C-Saunders]

I started looking into this because it seemed accessible, but I want to check my understanding, if possible, before continuing.

It seems like writing is initiated here and happens here, and a somewhat specific error message should result in the case of a missing permission.

Do you think the message should be more specific? Or maybe I am way off and looking in the wrong place?

[kinnison]

I think that it may be worthwhile to, instead of using ? in the first place, instead match on the result of utils::append_file() and make a better error report or use .chain_error() again to construct a more specific error message about amending the shell profile.