As per the feedback at https://github.com/google/fscrypt/issues/115
where users didn't understand that the recovery passphrase is important,
restore the original behavior where recovery passphrase generation
happens automatically without a prompt.  This applies to the case where
'fscrypt encrypt' is using a login protector on a non-root filesystem.

However, leave the --no-recovery option so that the recovery passphrase
can still be disabled if the user really wants to.  Also, clarify the
information provided about the recovery passphrase.

Update https://github.com/google/fscrypt/issues/115

These confuse the latest version of shellcheck into thinking that
functions which take no arguments actually take arguments, which
triggers a bunch of warnings like "Use func "$@" if function's $1 should
mean script's $1", which causes 'make lint' to fail.  These checks
aren't too useful, so just remove them.

Otherwise the cli tests fail when executed from GitHub Actions.

Apparently, on some distros 'su' doesn't preserve $PATH.  So, manually
export it in the command.  Also, ensure that the shell stays as bash.

This is needed for some of the CLI tests to pass in Travis CI.

When 'fscrypt status DIR' detects that a v1-encrypted directory is still
usable but its key seems to be absent, it shows the status as
"Unlocked: Partially (incompletely locked)".  But actually it can also
be the case that the directory is unlocked by another user.  Adjust the
status message accordingly.

This commit also fixes cli-tests/t_v1_policy.

The test user's user keyring is still linked into root's user keyring at
the end of the test.  This is making the test flaky, as there is a
failure that only occurs the first time it is run.  Fix the test to
restore the initial state.  This makes it consistently fail (to be fixed
by the next commit).

Use %q, in case the paths contain whitespace.  Also clean the directory
path to remove trailing slashes before appending the ".new" suffix.

Update https://github.com/google/fscrypt/issues/220

In checkEncryptable(), check whether the directory is already encrypted
before checking whether it's empty.

Also improve the error message for when a directory is nonempty.

Finally, translate keyring.ErrKeyAddedByOtherUsers and
keyring.ErrKeyFilesOpen into errors which include the directory.