setup: expose enumerated repo info

setup: expose enumerated repo info

We enumerate several different items as part of struct
repository_format, but then actually set up those values using the
global variables we've initialized from them.  Instead, let's pass a
pointer to the structure down to the code where we enumerate these
values, so we can later on use those values directly to perform setup.

This technique makes it easier for us to determine additional items
about the repository format (such as the hash algorithm) and then use
them for setup later on, without needing to add additional global
variables.  We can't avoid using the existing global variables since
they're intricately intertwined with how things work at the moment, but
this improves things for the future.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>