Add Czech (qwerty) keymap.

BUG=rhbz#1074879

Review URL: https://codereview.appspot.com/74520044
Update supported vala version to 0.20.

Review URL: https://codereview.appspot.com/76830043
Send panel input purpose.

gnome-shell gets input purpose so that disables IME with password mode.

Review URL: https://codereview.appspot.com/81770044
Keep track of content-type change after focus-in

This is an amendment to 6ca5ddb3.  As content-type (input-purpose and hints)
can change after focus-in, we should monitor the changes.

BUG=
R=takao.fujiwara1@gmail.com

Review URL: https://codereview.appspot.com/83920043
Fix leak in ibus_get_local_machine_id()

If /var/lib/dbus/machine-id does not exist but /etc/machine-id exists,
'error' will be set but will never be freed.

BUG=http://code.google.com/p/ibus/issues/detail?id=1701

Review URL: https://codereview.appspot.com/88770043
Patch from Christophe Fergeau <cfergeau@redhat.com>.
Change deprecated GtkHButtonBox to GtkButtonBox in ibus-setup.

Review URL: https://codereview.appspot.com/88850043
Do not show property panel by default.

Property panel sometimes hides text entry box on firefox in case
the mode is auto-hide because firefox does not provide the right
cursor locations and firefox does not update cursor locales
when preedit is updated so property panel hides text entry box
for a while and auto-hide is not useful with firefox and thunderbird.

TEST=gsettings reset org.freedesktop.ibus.panel show

Review URL: https://codereview.appspot.com/90480043
Do not move property panel with focus-in in case panel is always shown.

Review URL: https://codereview.appspot.com/98770043
Update translation zh_CN.po

Review URL: https://codereview.appspot.com/96740044
Release 1.5.7

Review URL: https://codereview.appspot.com/96800043
Fix not to switch engines by non-trigger keys.
Add libgnomekbd and load preload engines.
Reload preload engines until users customize the list.

The idea is, if users don't customize the preload_engines with ibus-setup,
users would prefer to load the system default engines again by login.
The gsettings value 'preload-engine-mode' is
IBUS_PRELOAD_ENGINE_MODE_USER by default but set
IBUS_PRELOAD_ENGINE_MODE_LANG_RELATIVE for the initial login.
If 'preload-engine-mode' is IBUS_PRELOAD_ENGINE_MODE_LANG_RELATIVE,
ibus-daemon loads the system preload engines by langs.
If 'preload-engine-mode' is IBUS_PRELOAD_ENGINE_MODE_USER,
ibus-daemon do not update the gsettings value 'preload-engines'
On the other hand, if users enable the customized engine checkbutton
on ibus-setup, ibus-setup sets 'preload-engine-mode' as
IBUS_PRELOAD_ENGINE_MODE_USER and users can customize the value
'preload-engines'.
Enable ibus-setup to show the frequently used languages only in IME list.