These are text files but their encoding does not depend on the locale.
Not all of them require utf8 but it is better to fix it at something
to remove potential unpredictability.

This is necessary on FreeBSD where no locale is set by default,
and apparently Python defaults not only the terminal encoding to the locale
but that of every text file. So without LOCALE environment it defaults text
file encoding to ASCII. This causes problems with e.g. `bitcoin.conf`.

Luckily the locale doesn't affect the default encoding for str.encode() and
bytes.decode() on Python 3, so this is the only change necessary.

Instead of calling sprintf for every byte, format the hex bytes
ourselves by help of HexStr and a reverse_iterator.

Zcash: Only the script we have.

We have several pieces of information about subtrees:
1) What their current directory contents is
2) What their directory contents was at the time of the last subtree merge
3) What the directory contents of the upstream project is in the commit referred to by the subtree merge.

Normally, all 3 should be identical. git-subtree-check.sh so far only compared (1) with (3) however.

Fix this by comparing all three, and give some more useful diff output in the case of mismatch.

The added benefit is that (1) and (2) can be compared without needing to see the upstream repository.

This partially reverts commit ab8e8b9

git-subtree-check fails if the directory is given with a trailing slash,
eg:

```
> test/lint/git-subtree-check.sh src/univalue/
ERROR: src/univalue/ is not a subtree
```

Shell autocompletes will add the trailing slash when autofilling the
path name, which will therefore cause the script to fail.

Just ignore any trailing slash.

These are external libraries, and it does not make sense to maintain an
otherwise-meaningless diff from upstream.

This partially reverts commit 1e6d183.

Fixes a false positive match to the locale-dependent trim function.