rebase: use read_oneliner()

rebase: use read_oneliner()

Since in sequencer.c, read_one() basically duplicates the functionality
of read_oneliner(), reduce code duplication by replacing read_one() with
read_oneliner().

This was done with the following Coccinelle script

	@@
	expression a, b;
	@@
	- read_one(a, b)
	+ !read_oneliner(b, a, READ_ONELINER_WARN_MISSING)

and long lines were manually broken up.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>