Fix engine exits with g_object_new when restart the engine.

Fix engine exits with g_object_new when restart the engine.

ibus <= 1.3 explicitly destroys engine when unset.  Which may result in
unloading the m17n type module and crash on restart.  This patch prevents
the type module from being unloaded.

BUG=https://bugzilla.redhat.com/show_bug.cgi?id=696476#c9
TEST=manual

Patch from Takao Fujiwara <takao.fujiwara1@gmail.com>

[Peng, 2011-04-20 16:05:40]

On 2011/04/20 07:20:59, Daiki Ueno wrote:

Could you explain why we need GTypeModule? Could we just register M17n engines
as static type? Sorry I forget the reason.

[Daiki Ueno, 2011-04-21 00:57:11]

On 2011/04/20 16:05:40, Peng wrote: 
> Could you explain why we need GTypeModule? Could we just register M17n engines
> as static type? Sorry I forget the reason.

I added GTypeModule so that M17N engine can specify GClassFinalizeFunc to
release memory used by MIM:
http://codereview.appspot.com/3270042/diff/1/src/engine.c#newcode19
Probably I worried about memory consumption by relatively large maps (e.g.
zh-cangjie).

However, since the finalizer no longer works with ibus-1.4, I agree with simply
using static types.  Even then we could move the MIM initialization/finalization
logic to IBusEngine#enable/disable.

I'll create a patch soon.

[Daiki Ueno, 2011-04-27 01:56:00]

Closing this as a new patch is posted at http://codereview.appspot.com/4431056/.