xterm driver doesn't ask xterm's version

[Paul "LeoNerd" Evans]

The driver uncondtionally splats query strings at startup, and other strings during operations, that might not be recognised depending on xterm version. While a real xterm will not have a problem with this, certain terminals that claim to be xterm that aren't (e.g. gnome-terminal) are known to cope very badly indeed with strings they don't recognise, up to and including having Pango/Cairo render a literal ESC byte into the graphical terminal area.

The xterm driver therefore ought to perform a version query on startup and only proceed to use these extra capabilities if it's quite sure the terminal will be OK with them.

This will require some research into what the actual terminals do in fact reply to version queries.