Merge branch 'ja/do-not-ask-needless-questions'

Git sometimes gives an advice in a rhetorical question that does
not require an answer, which can confuse new users and non native
speakers.  Attempt to rephrase them.

* ja/do-not-ask-needless-questions:
git-filter-branch: be more direct in an error message
read-tree -m: make error message for merging 0 trees less smart aleck
usability: don't ask questions if no reply is required

diff --cc Documentation/git-read-tree.txt
Simple merge

diff --cc builtin/am.c
Simple merge

diff --cc builtin/checkout.c
Simple merge

diff --cc builtin/read-tree.c
Simple merge