Merge branch '2136_status_window'
* 2136_status_window:
mcedit: apply status message for file load process.
mcedit: apply status message for search process.
(edit_buffer_calc_percent): new editor buffer API.
mcviewer: apply status message for search process.
mcviewer: refactoring of percentage display.
Apply status message for directory size calculation.
(label_set_textv): new WLabel API.
(simple_status_msg_t): simple status message with label and 'Abort' button.
Create status dialog window to interrupt long-time operations.
Ticket #2136: implement user-friendly interruption of long-time operations.