pager: do allow spawning pager recursively

This reverts commit 88e8f908f2b0c56f9ccf8134d8ff9f689af9cc84, which tried to allow GIT_PAGER="git -p column --mode='dense color'" git -p branch and still wanted to avoid "git -p column" to invoke itself. However, this falls into "don't do that -p then" category. In particular, inside "git log", with results going through less, a potentially interesting commit may be found and from there inside "less", the user may want to execute "git show <commit>". Before the commit being reverted, this used to show the patch in less but it no longer does. Signed-off-by: Jörn Engel <joern@logfs.org> Reviewed-by: Jeff King <peff@peff.net> Reviewed-by: Matthieu Moy <Matthieu.Moy@imag.fr> Acked-by: Duy Nguyen <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>