for-each-ref: add new option to include root refs

for-each-ref: add new option to include root refs

The git-for-each-ref(1) command doesn't provide a way to print root refs
i.e pseudorefs and HEAD with the regular "refs/" prefixed refs.

This commit adds a new option "--include-root-refs" to
git-for-each-ref(1). When used this would also print pseudorefs and HEAD
for the current worktree.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>