6df42ab (Add global and system-wide gitattributes, 2010-09-01) forgot
to quote one instance of $HOME in the tests. This would be valid
according to POSIX, but bash 4 helpfully declines to execute the
command in question with an "ambiguous redirection" error.
Signed-off-by: Thomas Rast <trast@student.ethz.ch> Signed-off-by: Junio C Hamano <gitster@pobox.com>