kde: Enable ki18n keywords by default

kde: Enable ki18n keywords by default

* gettext-tools/src/x-c.c (init_flag_table_kde): New function.
(additional_keywords_kde): New variable.
(activate_additional_keywords_kde): New function.
(init_keywords): Optional addition of KDE-specific keywords.
* gettext-tools/src/x-c.h (init_flag_table_kde): New function declaration.
(activate_additional_keywords_kde): New function declaration.
* gettext-tools/src/xgettext.c (main): Invoke addition of KDE-specific
keywords when language is C++ with KDE.

* NEWS: Mention --kde behavior change.