repository: move global r_f_p_c to repo struct

repository: move global r_f_p_c to repo struct

Move repository_format_partial_clone, which is currently a global
variable, into struct repository. (Full support for per-repository
partial clone config will be done in a subsequent commit - this is split
into its own commit because of the extent of the changes needed.)

The new repo-specific variable cannot be set in
check_repository_format_gently() (as is currently), because that
function does not know which repo it is operating on (or even whether
the value is important); therefore this responsibility is delegated to
the outermost caller that knows. Of all the outermost callers that know
(found by looking at all functions that call clear_repository_format()),
I looked at those that either read from the main Git directory or write
into a struct repository. These callers have been modified accordingly
(write to the_repository in the former case and write to the given
struct repository in the latter case).

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>