Allow display names to be arbitrary paths [v2]

This lets the local listening socket live in a protected directory
where other users cannot spoof it.

Signed-off-by: Keith Packard <keithp@keithp.com>

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v2:
	Update comment in VerifyDisplayName
5 jobs for listen-path in 6 minutes and 26 seconds (queued for 19 seconds)
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  Docker Image
passed debian-buster #12462507

00:01:34

 
  Build And Test
passed autotools #12462508

00:04:51

passed meson #12462509

00:01:50

passed meson-noglamor #12462510

00:02:11

passed mingw-cross-build #12462511

00:00:39