Created attachment 715892 [details]
bracketcompletion: use key release event to work with input method

From: bgo#778737 https://bugzilla.gnome.org/show_bug.cgi?id=778737

Some user reported that ibus-libpinyin/ibus-pinyin doesn't work
with gedit plugin bracket completion.

I tried to modify the gedit plugin code, it seems work now.
Please review it, thanks!

How to reproduce it:
1. Switch to C/C++ mode, press "(", bracket completion works.
2. Switch input method to "Intelligent Pinyin" or "Pinyin", it doesn't work.