gcr-prompt-dialog: Allow the use of mnemonics in the choice label
pinentry-gnome3 tries to use this, but gets an ugly "_Save in password manager" instead.
Fixes: https://bugzilla.gnome.org/show_bug.cgi?id=752328
We have been applying this in Debian since 2017. I think it's only relevant to uses of gcr that do not involve GNOME Shell, so mostly that means GNOME Flashback, Unity and other GNOME forks.
A similar bug in GNOME Shell environments was fixed in gnome-shell@59a18c4e (https://bugzilla.gnome.org/show_bug.cgi?id=750465).
Edited by Simon McVittie