Added time-error signal - NB#22155
* hildon-widgets/hildon-time-editor.c:
(hildon_time_editor_class_init): added time-error signal
(validated_conversion): added 'error_code' output parameter.
(hildon_time_editor_real_validate): use 'error_code' and trigger
'time-error' signal when apprpriate.
(highlight_callback): avoid revalidation
* hildon-widgets/hildon-time-editor.h (HildonTimeEditorErrorType):
new enumerative type for error types
(_HildonTimeEditorClass): added time_error signal
* hildon-widgets/Makefile.am (hildon-libs-enum-types.c): added time-editor.h