git.c: ignore pager.* when launching builtin as dashed external

When running, e.g., `git -c alias.bar=foo bar`, we expand the alias and execute `git-foo` as a dashed external. This is true even if git foo is a builtin. That is on purpose, and is motivated in a comment which was added in commit 441981bc ("git: simplify environment save/restore logic", 2016-01-26). Shortly before we launch a dashed external, and unless we have already found out whether we should use a pager, we check `pager.foo`. This was added in commit 92058e4d ("support pager.* for external commands", 2011-08-18). If the dashed external is a builtin, this does not match that commit's intention and is arguably wrong, since it would be cleaner if we let the "dashed external builtin" handle `pager.foo`. This has not mattered in practice, but a recent patch taught `git-tag` to ignore `pager.tag` under certain circumstances. But, when started using an alias, it doesn't get the chance to do so, as outlined above. That recent patch added a test to document this breakage. Do not check `pager.foo` before launching a builtin as a dashed external, i.e., if we recognize the name of the external as a builtin. Change the test to use `test_expect_success`. Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>