Update #272

Set the terminal to raw mode *before* printing the prompt.
Otherwise the user (or the automated test) might enter the
passphrase before the terminal gets put into raw mode.

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

On an "incompletely locked" directory, isDirUnlockedHeuristic() is
supposed to return true, but on Linux v5.10-rc1 and later it returns
false since now creating a subdirectory fails rather than succeeds.
This change was intentional, so make isDirUnlockedHeuristic() apply a
second heuristic too: also return true if any filenames in the directory
don't appear to be valid no-key names.

This fixes cli-tests/t_v1_encrypt on Linux v5.10-rc1 and later.

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.

statfs.Bsize actually has platform-dependent type, despite the Go
documentation listing it as int64.  Fix the build for 32-bit platforms
by casting it to int64.

Resolves https://github.com/google/fscrypt/issues/233

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.