autocompletion should not remember words smaller than 3 or 4 letters

[jquelin]

autocompletion is really great. however, sometimes it proposes to complete with words of 3 characters...

i think it should not remember those words, since autocompletion in that case is more a burden than a help.

warning: this does not mean that it shouldn't propose completion ideas at the 2nd character! :)

[Sewi]

Configurable from r9243