t1308: do not get fooled by symbolic links to the source tree

t1308: do not get fooled by symbolic links to the source tree

When your $PWD does not match $(/bin/pwd), e.g. you have your copy
of the git source tree in one place, point it with a symbolic link,
and then "cd" to that symbolic link before running 'make test', one
of the tests in t1308 expects that the per-user configuration was
reported to have been read from the true path (i.e. relative to the
target of such a symbolic link), but the test-config program reports
a path relative to $PWD (i.e. the symbolic link).

Instead, expect a path relative to $HOME (aka $TRASH_DIRECTORY), as
per-user configuration is read from $HOME/.gitconfig and the test
framework sets these shell variables up in such a way to avoid this
problem.

Signed-off-by: Junio C Hamano <gitster@pobox.com>