Set longer fetch timeout for SHA/tag response

[janbrasna]

Resolves #419

Server does the work anyways, so it's too bad the client raises an error earlier than the results arrive.

(This also tweaks some wording to make the eventual corner cases more comprehensible.)

[stevejalim]

r+wc

But of course we need an r+ from Peter to really count :)

[janbrasna]

I have also included some general wording/formatting tweaks around error messaging with this, as I was often mislead by the errors reported when investigating this. Should be generally uncontroversial, here's one example I though could benefit from formatting to separate the actual content from the message:

(before:)

(after:)