Please fill in this template when reporting a bug, unless you know what you
are doing.
Description of Problem:

When using input method, it records all
pre-editing operations and shows up all at undo operation.
Those are redundant, never on Microsoft or other proprietary
standard, nor on traditional/modern apps of UN*X systems.

Steps to reproduce the problem:
1. Use your favorite GTK+2 immodule which uses preedit.
   Or try im-euro if you are not CJK.
   http://www.gnomefiles.org/app.php?soft_id=330
   (Below steps are for im-euro
2. Shift+Space to start euro input mode.
3. Press 'e' 'u' 'r' 'o'
4. Press space
5. Press return to commit
6. Press Undo button and 'euro' on the app
7. Press Undo button and nothing on the app
8. Press Undo button and 'eur' on the app
9. Press Undo button and nothing on the app
10. Press Undo button and 'eu' on the app
11. Press Undo button and nothing on the app
12. Press Undo button and 'e' on the app
etc

Actual Results:
All preedit operations are for undo.


Expected Results:
No preedit operations are for undo.


How often does this happen? 
Always

Additional Information:
The following patch adds freeze/unfreeze function to
HtmlUndo class, to prevent recording undo action in
gtk_html_im_preedit_changed_cb().

gtk_html_im_commit_cb() has a fix, but this fix needs
some description. If an immodule clears the preedit string
before commit, gtk_html_im_commit_cb() doesn't need this fix.
But we cannot assume all immodules behave like that. And maybe
most immodules do not clear preedit string before commit because
of the implementation reason. A "preedit_changed" callback
usually returns the copy of the preedit string buffer, and a
"commit" callback also uses it. So developer don't want to clear
preedit string buffer before commit. You might feel it's
difficult to see the point, but if you implement a CJK immodule,
you'll soon understand. Anyway, gtkhtml should not restrict
each immodule behavior, but should support many variations of
immodules.

And I think some people might feel disagree to deleting
preedit string in gtk_html_im_commit_cb(). Some input method
support the style of commit while it has keep a part of
preedit string. (Canna's C-j key combo really works like so.)
But the original meaning of preedit is to let user choose the
candidate for commit, so we should be able to assume immodules
will call "preedit_changed" after commit, if they want to have
preedit string after commit.