Pabbrev, ido and iswitchb extensions

- pabbrev already lightly tested, but not so improving from dabbrev. So not used for the moment.

- ido and iswitchb must be checked, to rapdily switch buffers.

--- Update

ido installed : is greate. Replaced "C-x b" command to type a sequence to get the buffer.

--- Update2

Ido not so great, because with it cannot update file path (bugs ?)
So has been switched to iswicthb, and is OK, with additional arrow bindings found on
http://www.emacswiki.org/cgi-bin/wiki/IswitchBuffers