fast-import: use write_idx_file() instead of custom code
fast-import: use write_idx_file() instead of custom code

This allows for the creation of pack index version 2 with its object
CRC and the possibility for a pack to be larger than 4 GB.

Signed-off-by: Nicolas Pitre <d659c10e27d52b00987b65e85d99bce5480adcae@fluxnic.net>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git