Tweak magit-find-file* docstrings.

Capitalize FILE, leave out REV.

Any suggestions for how to put it back in concisely?
Tweak magit-request-pull docstring.
Tweak magit-merge-state docstring.
Tweak magit-maybe-save-head-message's docstring.
Tweak magit-notes-prune docstring.

Not sure I got this right... for some reason my Elisp config wouldn't
let me tab. Will have to track that down.