fix failing quickcheck properties

QuickCheck 2.10 found a counterexample eg "\929184" broke the property.

As far as I can tell, Git.Filename is matching how git handles encoding
of strange high unicode characters in filenames for display. Git does
not display high unicode characters, and instead displays the C-style
escaped form of each byte. This is ambiguous, but since git is not
unicode aware, it doesn't need to roundtrip parse it.

So, making Git.FileName's roundtrip test only chars < 256 seems fine.

Utility.Format.format uses encode_c, in order to mimic git, so that's
ok.

Utility.Format.gen uses decode_c, but only so that stuff like "\n"
in the format string is handled. If the format string contains C-style
octal escapes, they will be converted to ascii characters, and not
combined into unicode characters, but that should not be a problem.
If the user wants unicode characters, they can include them in the
format string, without escaping them.

Finally, decode_c is used by Utility.Gpg.secretKeys, because gpg
--with-colons hex-escapes some characters in particular ':' and '\\'.
gpg passes unicode through, so this use of decode_c is not a problem.

This commit was sponsored by Henrik Riomar on Patreon.

Utility/Gpg.hs

@@ -184,6 +184,9 @@ secretKeys cmd = catchDefaultIO M.empty makemap
 	params = [Param "--with-colons", Param "--list-secret-keys", Param "--fixed-list-mode"]
 	parse = extract [] Nothing . map (splitc ':')
 	extract c (Just keyid) (("uid":_:_:_:_:_:_:_:_:userid:_):rest) =
+		-- If the userid contains a ":" or a few other special
+		-- characters, gpg will hex-escape it. Use decode_c to
+		-- undo.
 		extract ((keyid, decode_c userid):c) Nothing rest
 	extract c (Just keyid) rest@(("sec":_):_) =
 		extract ((keyid, ""):c) Nothing rest