test_fsh() should quote its arguments before passing them
to `eval` otherwise there are problems when the arguments
contain spaces.

For example when running the following program:

```
#!/bin/sh

. ./ipfs-test-lib.sh

die () {
    printf >&2 "%s\n" "$@"
    exit 1
}

DIR1="test dir 1"
DIR2="test dir 2"

mkdir "$DIR1" "$DIR2" || die "Could not mkdir '$DIR1' '$DIR2'"

echo "in dir 1" >"$DIR1/file1" || die "Could not write into '$DIR1/file1'"
echo "in dir 2" >"$DIR2/file2" || die "Could not write into '$DIR2/file2'"

if test_cmp "$DIR1/file1" "$DIR2/file2"
then
    echo "test_cmp succeeded!"
else
    echo "test_cmp failed!"
fi

rm -rf "$DIR1" "$DIR2" || die "Could not rm -rf '$DIR1' '$DIR2'"

```

we get:

```
> diff -u test dir 1/file1 test dir 2/file2
diff: extra operand '1/file1'
diff: Try 'diff --help' for more information.

test_cmp failed!
```

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>