This kind of mistakes can make Nautilus crash, as seen in
<https://bugzilla.gnome.org/show_bug.cgi?id=763486>, and gettext's
msgfmt -c won't catch them, because %B is not proper c-format.
This commit fixes them like this:
1) A real fix is applied when the error is obvious to a non-speaker
of the language (missing %, %s instead of %B, etc.)
2) The string is marked as fuzzy if the solution needs attention
of a native speaker.
3) The string is deleted if it's obsolete.
