pre-receive: adjust pack-*.idx permissions too
We have been adjusting the permissions of pack-*.pack files for some
time now at pre-receive time. Doing so makes it possible to perform
repository maintenance more easily and reliably by allowing packs that
have been pushed by a chroot jail owner to be manipulated by the
Girocco maintenance user.
Expand that to include all pack extensions. In order to rename pack
files the pack-*.idx also needs group write permission or else the
Girocco maintenance user will be forced to copy rather than just
hard-link during the rename operation which is much less efficient.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>