bug#43866: 26.3; italian postfix additions

[Francesco Potortì]

>> E= -> €
>> 
>> Typewriter-style italian characters. 
>
>If they really are typewriter-style, wouldn't C= make more sense? E
>overstruck with = would just be a smudgy mess even if typed on a
>beautiful Olivetti.

The euro sign under E is on many Italian keyboards, so that sounds
natural to me.  Never seen C= as a shortcut, my X understands e= and E=
but not c= or C=.
>
>Both C= and E= seem to work as X11 compose pairs. We could include both.
>That is, c=, C=, e=, E=, and c==, C==, e==, E== as the literal cases.

I would not include c= and C=.  I would not include e= either.  These
things are very annoying unless they are really useful, so better just
include what's really needed and nothing more.