The sharer and repo were being taken and used as is to check push permissions,
which is how it's supposed to be, *but* they were also being used as is to
build the repo path! So sharer and repo names that aren't all lowercase were
getting "No such repository" errors when trying to push.
I changed `RepoSpec` to hold `ShrIdent` and `RpIdent` instead of plain `Text`,
to avoid confusions like that and be clear and explicit about the
representation, and failures to find a repo after verifying it against the DB
are now logged as errors to help with debugging.
I hope this fixes the problem.
This is a lot of code, better save now than sorry later when something
gets deleted by mistake.
Either way, the code will move later - once tested and organized
properly - into its own package.
