The problem with this is that "git -p column" also has $GIT_PAGER set so
the pager runs itself again as another pager. The end result is an
infinite loop of forking. Other git commands have the same problem if
being abused this way.
Check if $GIT_PAGER is already set and stop launching another pager.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>