There're two issues in GdkQuartzView's NSTextInputClient implementation
causes this bug.

1. The -(NSRange)selectedRange should not return [NSNotFound, 0] if
   there's no selection. The accented character window will not show
   if returned NSRange's location is NSNotFound. Instead of that, the
   NSRange's location should be the caret position in the text input
   buffer.

2. The accented character window will invoke
   -(void)insertText:replacementRange: with non-empty replacement
   range, to replace non-accented character with accented character
   after user select it from accented character window. This case is
   not implemented in original code. Here I use another gobject data
   to pass the information to input module and convert it into
   'delete-surrounding' event.

Besides these, there's another bug cause gtk_im_context_filter_keypress()
return wrong value while user press and hold a key. When user press
and hold a key, the accented character window will consume the
repeating key down event. Is this case, gtk_im_context_filter_keypress()
should return TRUE, indicate the key press is filtered by input
method module. But it will return FALSE because
gtk_im_context_filter_keypress() assume that every key press event
will generate some text from input method module.

Fixes #1618