t0003: use named parameters in attr_check()

t0003: use named parameters in attr_check()

We had named the parameters in attr_check() but $2 was being used
instead of $expect. Make all variable accesses in attr_check() use named
variables instead of numbered arguments for clarity.

While we're at it, add variable assignments to the &&-chain. These
aren't ever expected to fail but if a future developer ever adds some
code above the assignments and they could fail in some way, the intact
&&-chain will ensure that the failure is caught.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>