read-command, read-variable, read-buffer implemented in C

["Óscar Fuentes" <ofv@wanadoo.es>]

I guess it is an historical artifact due to performance concerns, but
now it doesn't make much sense anymore, right?

Some extensions need to jump through hoops because of this. For using
Ido (almost) everywhere it would be enough to advise `completing-read',
which is what those functions end using, but as advices are not
effective for functions defined in C when they are called from other C
functions, extensions such as ido-hacks are forced to advise the
functions that call read-*, which is quite a hassle.

Or I'm wrong wrt adivising C functions and overlooking other
considerations?