Support extended clipboard transfers

Implements support in both client and server for the extended
clipboard format first seen in UltraVNC. Currently only implements
text handling, but that is still an improvement as it extends the
clipboard from ISO 8859-1 to full Unicode.
diff --git a/vncviewer/vncviewer.man b/vncviewer/vncviewer.man
index ebfe772..f93e096 100644
--- a/vncviewer/vncviewer.man
+++ b/vncviewer/vncviewer.man
@@ -182,6 +182,11 @@
 Default is on.
 .
 .TP
+.B \-MaxCutText \fIbytes\fP
+The maximum size of a clipboard update that will be accepted from a server.
+Default is \fB262144\fP.
+.
+.TP
 .B \-SendClipboard
 Send clipboard changes to the server. Default is on.
 .