pager: Work around window resizing bug in 'less'

pager: Work around window resizing bug in 'less'

If you resize the terminal while less is waiting for input, less
will exit entirely without even showing the output. This is very
noticeable if you do something like "git diff" on a big and
cold-cache tree and git takes a few seconds to think, and then
you resize the window while it's preparing. Boom. No output AT
ALL.

The way to reproduce the problem is to do some pager operation
that takes a while in git, and resizing the window while git is
thinking about the output.  Try

	git diff --stat v2.6.12..

in the kernel tree to do something where it takes a while for git to start
outputting information.

Signed-off-by: Junio C Hamano <junkio@cox.net>