git-*-verify: sanitize log messages before output

git-*-verify: sanitize log messages before output

Part of the information in the log message comes from a remote
client.  The point of logging is not only to include successful
requests, but also denied requests.

That means the information from the remote client contained within
a denied request log message has failed validation.

Consider that for a moment.  It could literally be *ANY* sequence
of bytes.

Exhibit an abundance of caution and transform any bytes which are
not in the range \x20-\x7E (the printable characters) and are not
the final newline character (\x0A) into '?' characters before output.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>