To libify the apply functionality the 'patch_input_file' variable should
not be static and global to the file. Let's move it into
'struct apply_state'.
Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>