Achieving consistent key translations in terminal and GTK

[Leo Alekseyev <dnquark@gmail.com>]

In terminal, the bindings for keys {enter, tab, escape} are {RET, TAB,
ESC}.  Under GTK, they are {<return>, <tab>, <escape>}.  This leads to
the following annoyances:

- custom keybindings involving these have to be defined twice, e.g.
once for "RET" and once for "<return>" for things to work both in
terminal and GTK
- some modes apparently fail to do this, overload one form (e.g.
"TAB") but not another, forcing me to go and fix it manually

Is there a way to normalize the keybindings so that things work the
same under terminal and GTK with no further effort?

Furthermore, is it possible to achieve this while preserving (in the
terminal) the distinction between e.g. C-[ and physical escape key, or
C-i and physical tab key (under GTK, these send "ESC" vs <escape> and
"TAB" vs <tab> respectively).

--Leo