Use XDG_ENVIRONMENT_TYPE to switch to CLIPBOARD

It appears that XDG_ENVIRONMENT_TYPE will always equal "wayland"
when XWayland is in use, so when we see that, switch to CLIPBOARD
instead of PRIMARY.  This should fix WSL and ChromeOS, and be
irritating on GNOME, so it's a win all around.

src/conio/x_events.c

@@ -327,6 +327,7 @@ initialize_atoms(void)
 	Atom atom;
 	struct AtomDef *ad;
 	long offset;
+	const char *evar;
 
 	supported_standards |= (1 << UTF8_ATOM);
 	supported_standards |= (1 << ICCCM_ATOM);
@@ -424,10 +425,15 @@ initialize_atoms(void)
 	}
 
 	/*
-	 * ChromeOS doesn't do anything reasonable with PRIMARY...
-	 * Hack in use of CLIPBOARD instead.
+	 * Wayland sucks, use CLIPBOARD instead of PRIMARY
+	 * This will annoy users in Wayland environments where
+	 * PRIMARY is properly supported (apparently GNOME)
+	 * but GNOME is why I'm not writing a Wayland bakend
+	 * right now anyway (no server-side decorations) so
+	 * they can suck it.
 	 */
-	if (wm_wm_name != NULL && strcmp(wm_wm_name, "Sommelier") == 0) {
+	evar = getenv("XDG_SESSION_TYPE");
+	if (evar && strcmp(evar, "wayland")) {
 		if (A(CLIPBOARD) != None)
 			copy_paste_selection = A(CLIPBOARD);
 	}