Also, capture all stderr and stdout but pass "-q".
This way we get to see error messages if there are any, or
spurious output when there should be none due to "-q".
We (actually, go-fuse) used to call Chown() instead of Lchown()
which meant that the operation would fail on dangling symlinks.
Fix this by calling os.Lchown() ourself. Also add a test case
for this.
Running these tests from integration_tests' TestMain() was awkward
because they were run twice with unchanged settings.
integration_tests tests everything with OpenSSL and with native
Go crypto, but this does not take affect for the example filesystems.
To make this work, test_helpers is also split into its own package.
