ioemu: fix VNC altgr-insert behavior

ioemu: fix VNC altgr-insert behavior

When access to a Xen DomU (Linux) from a VNC client in Windows, alt-gr
key is not working properly with Spanish keyboard. When Alt + another
key pressed, vncserver receives Altgr down, Altgr up and key down
messages in order, that causes incorrect output.

With following patch, when vncerver receives key down message, it
first check if the keysym needs altgr modifer, if it needs altgr
modifier but altgr is not 'down', sending altgr keycode before sending
key keycode.

Signed-off-by: Chunyan Liu <cyliu@novell.com>