[FIX] bad interaction of editable list with IME

IME are ways to input language which can't trivially map to a keyboard
(e.g. CJK language) with a standard-ish keyboard. For japanese IME
this is done by entering text phonetically: text is entered in romaji
and automatically converted to hiragana (or katakana) when it matches
the transcription a japanese syllable (~phoneme?) e.g. to (と). The
text is then split and reprocessed with sequences of hiragana being
converted to kanji (or not), and the possibility to pick the right
kanji when multiple kanji match e.g. for "Tokyo" toukyou -> とうきょう
-> 東京.

But to do the edition, keyboard keys are used. For the japanese IMEs
(tested on Windows, OSX and Linux) [Space] will do the initial
conversion from kana to kanji (and allow selecting an other conversion
or a different kana split) and [Return] will validate the current
conversion (removing the underline marking "unvalidated" kana or kanji
groups).

And that's where the problem hit: IME + browser combinations may or
may not suppress part of all of the event. Firefox will trigger a
keydown of the key which "starts" IME input (e.g. "t") and will
trigger a keyup for the validation key (return), except on Linux where
the initial keydown is suppressed. Inbetween these, it will fire no
keydown, keyup or keypress event but will fire input events (at least
on an input element) every time the displayed text changes.

Meanwhile webkit browsers will, for each press on the keyboard during
IME,

* trigger a keydown with the keyCode 229
* trigger a keyup event with the keycode of the key which was actually
  hit
* trigger input events every time the displayed text changes

This include meta-operation uses of [Space] and [Return].

MSIE has the same behavior (including triggering the input event), but
the keydown event is augmented with ``key`` and ``char`` attributes
providing the character matching the key hit to trigger the change.

Although the triggering of the input even is useless for the purpose
of the editable list (especially here, the purpose of validating a
list row with [Return] one fact stands out: keypress is never
triggered during IME operations, hitting the [Return] key outside of
IME will trigger keydow, keypress, keyup but doing so during IME will
only trigger the first and last.

Thus by changing the binding from keyup (return) to keypress (return)
for a line validation, spurious validation during IME text entry
should be avoided. This seems to work correctly on MSIE (Windows),
Firefox (Windows, OSX, Linux), Chrome (Windows, OSX, Linux) and Safari
(OSX), after testing in IE9, IE10, Chrome 31, Firefox 25 and Safari 7,
and a quick test on a task's o2m did not reveal any regression.

note: not all differences between various browser/os combinations were
inspected in details, there may well be further differences which were
not noticed or not relevant to this precise issue.
[MERGE] fixes for non-direct IME