object-name: turn INTERPRET_BRANCH_* constants into enum values

object-name: turn INTERPRET_BRANCH_* constants into enum values

Replace the INTERPRET_BRANCH_* preprocessor constants with enum
values and use that type where these flags are stored or passed
around.

These flags describe which kinds of branches may be considered during
branch-name interpretation, so represent them as an enum describing
branch kinds while keeping the existing bitmask semantics and
INTERPRET_BRANCH_* element names.

Signed-off-by: Jialong Wang <jerrywang183@yahoo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>