Fix behavior of Ctrl-[0-9]

Fix behavior of Ctrl-[0-9]

Patch contributed by Steven Luo. steven+android@steven676.net

Steven writes:

In xterm on my Debian system, the Ctrl-[0-9] combinations appear to map
to the following:

Ctrl-2: ^@ (NUL)
Ctrl-3: ^[ (ESC)
Ctrl-4: ^\
Ctrl-5: ^]
Ctrl-6: ^^
Ctrl-7: ^_
Ctrl-8: \177 (DEL)

Ctrl-1, Ctrl-9, and Ctrl-0 appear to send 1, 9, and 0 respectively.

I have no idea whether anyone actually seriously uses these, but make
these key combinations behave in that manner, and remove the bogus
Ctrl-[0-9] and superfluous Fn-[234] combos.