branch: respect `pager.branch` in list-mode only

branch: respect `pager.branch` in list-mode only

Similar to de121ffe5 (tag: respect `pager.tag` in list-mode only,
2017-08-02), use the DELAY_PAGER_CONFIG-mechanism to only respect
`pager.branch` when we are listing branches.

We have two possibilities of generalizing what that earlier commit made
to `git tag`. One is to interpret, e.g., --set-upstream-to as "it does
not use an editor, so we should page". Another, the one taken by this
commit, is to say "it does not list, so let's not page". That is in line
with the approach of the series on `pager.tag` and in particular the
wording in Documentation/git-tag.txt, which this commit reuses for
git-branch.txt.

This fixes the failing test added in the previous commit. Also adapt the
test for whether `git branch --set-upstream-to` respects `pager.branch`.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>