sha1-name: replace unsigned int with option struct

sha1-name: replace unsigned int with option struct

In preparation for a future patch adding a boolean parameter to
repo_interpret_branch_name(), which might be easily confused with an
existing unsigned int parameter, refactor repo_interpret_branch_name()
to take an option struct instead of the unsigned int parameter.

The static function interpret_branch_mark() is also updated to take the
option struct in preparation for that future patch, since it will also
make use of the to-be-introduced boolean parameter.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>