git-quiltimport: preserve standard input to be able to read user input

git-quiltimport: preserve standard input to be able to read user input

When run without --author and it fails to determine an author, git
quiltimport tries `read patch_author` to get user input, but standard
input has been redirected to the patch series file.  This commit lets
quiltimport read the series file through file descriptor 3 so that the
standard input is preserved.

Reported by Uwe Kleine-König through http://bugs.debian.org/515910

Signed-off-by: Gerrit Pape <pape@smarden.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>