Add more possible paths for Xsession, depending on which display manager is
installed.  We need an Xsession that executes its command line parameters, so
leave xinit last.

See also https://bugs.gentoo.org/746227 and https://bugs.gentoo.org/936475

--- a/unix/vncserver/vncserver.in
+++ b/unix/vncserver/vncserver.in
@@ -437,11 +437,14 @@
 	die "$prog: couldn't find \"$cmd\" on your PATH.\n";
     }
 
-    foreach $cmd ("/etc/X11/xinit/Xsession", "/etc/X11/Xsession") {
-        if (-x "$cmd") {
-            $Xsession = $cmd;
-            last;
-        }
+    $Xsession=$ENV{TIGERVNC_XSESSION_FILE};
+    if (not defined $Xsession) {
+	foreach $cmd ("/usr/share/sddm/scripts/Xsession", "/etc/gdm/Xsession", "/etc/lightdm/Xsession", "/usr/share/slim/Xsession", "/etc/X11/Sessions/Xsession", "/etc/X11/xinit/Xsession", "/etc/X11/Xsession") {
+	    if (-r "$cmd") {
+		$Xsession = $cmd;
+		last;
+	    }
+	}
     }
     if (not defined $Xsession) {
         die "$prog: Couldn't find suitable Xsession.\n";