Include unix socket in vncviewer usage

We've had support for unix sockets for a while now. Make sure this
is reflected in the -help output and the man page.

Also make some minor tweaks to the section to get everything in
sync with reality.
diff --git a/vncviewer/vncviewer.cxx b/vncviewer/vncviewer.cxx
index f076565..8d79510 100644
--- a/vncviewer/vncviewer.cxx
+++ b/vncviewer/vncviewer.cxx
@@ -348,10 +348,19 @@
 #endif
 
   fprintf(stderr,
-          "\nusage: %s [parameters] [host:displayNum] [parameters]\n"
-          "       %s [parameters] -listen [port] [parameters]\n"
+          "\n"
+          "usage: %s [parameters] [host][:displayNum]\n"
+          "       %s [parameters] [host][::port]\n"
+#ifndef WIN32
+          "       %s [parameters] [unix socket]\n"
+#endif
+          "       %s [parameters] -listen [port]\n"
           "       %s [parameters] [.tigervnc file]\n",
-          programName, programName, programName);
+          programName, programName,
+#ifndef WIN32
+          programName,
+#endif
+          programName, programName);
   fprintf(stderr,"\n"
           "Parameters can be turned on with -<param> or off with -<param>=0\n"
           "Parameters which take a value can be specified as "