t/t7008: workaround broken handling of \000 by printf on IRIX

t/t7008: workaround broken handling of \000 by printf on IRIX

On IRIX 6.5, the printf utility in /usr/bin does not appear to handle the
\ddd notation according to POSIX.  This printf appears to halt processing
of the string argument and ignore any additional characters in the string.
Work around this flaw by replacing the \000's with 'Q' and using the
q_to_nul helper function provided by test-lib.sh

This problem with printf is not apparent when using the Bash shell since
Bash implements a POSIX compatible printf function internally.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>