Input methods that compose multiple characters don't work properly (only the first character is inserted)

[smathot]

Certain input methods, such as Japanese (see this discussion) and Pinyin Chinese, work such that multiple characters can be composed and inserted at once. In OpenSesame, this doesn't work properly, because only the first character is accepted.

In the legacy and xpyriment backend, this is because the separate characters are represented as separate events, and the input loop assumes that there is only one such event. How this works in the psycho backend needs to be tested.