On Windows, it is not possible to rename or remove a directory that has
open files. 'revert --abort' renamed .git/sequencer when it still had
.git/sequencer/head open. Close the file as early as possible to allow
the rename operation on Windows.
Signed-off-by: Johannes Sixt <j6t@kdbg.org> Acked-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>