run-tests.py: fix diff output when test-foo.out doesn't exist.
Previously, if test-foo.out doesn't exist and test-foo outputs
something, the first line of the diff will look like this:
-+changeset: 0:0acdaf898367
(note the leading "-")
#!/bin/sh
#
mkdir t
cd t
hg init
echo 0 > a
echo 0 > b
echo 0 > t.h
mkdir t
echo 0 > t/x
hg ci -A -m m -d "1000000 0"
touch nottracked
hg locate a
hg locate NONEXISTENT
hg locate
hg rm a
hg ci -m m -d "1000000 0"
hg locate a
hg locate NONEXISTENT
hg locate
hg locate -r 0 a
hg locate -r 0 NONEXISTENT
hg locate -r 0
echo % -I/-X with relative path should work
cd t
hg locate
hg locate -I ../t
# test issue294
cd ..
rm -rf t
hg locate t