Fix API compatibility issue in ibus_config_new.

Fix API compatibility issue in ibus_config_new.

On ibus-1.3, ibus_config_new returns NULL when ibus-gconf is not started yet, but on 1.4 it returns a valid, non-NULL IBusConfig object. This patch fixes the discrepancy by changing the behavior of ibus_config_new of 1.4.

If we don't return NULL when ibus-gconf does not exist, successive calls e.g. ibus_config_set_value will fail with a cryptic error message like 'IBUS-WARNING **: org.freedesktop.IBus.Config.SetValue: Cannot invoke method; proxy is for a well-known name without an owner and proxy was constructed with the G_DBUS_PROXY_FLAGS_DO_NOT_AUTO_START flag'. I believe returning NULL makes it easier to use the ibusconfig.h APIs.

Please note that this patch is particularly important for Chromium OS. Since ibus_config_new is called shortly after ibus-daemon starts on the OS, ibus_config_new is sometimes called before ibus-memconf starts actually. This change helps the glue between chrome and ibus-daemon to remain clean.

BUG=none
TEST=manually on Chromium OS

[Yusuke Sato, 2010-12-26 17:08:51]

(this change is for the master branch as well)

[Peng, 2010-12-26 17:47:00]

On 2010/12/26 17:08:51, Yusuke Sato wrote:
> (this change is for the master branch as well)

LGTM. Thanks