Fix loosing oldest elements of histories
Merge branch 'fix-loosing-old-history-items'

Fix situation when oldest elements of histories were not available
even though they were present in vifminfo file.
Pass Ctrl-C to child process
Poll file descriptor for better interactivity
Extract cancelling functionality into functions
Finish updating background_and_capture()
Move cancel_requested() => ui_cancel_requested()
Move wait_data_from() => wait_for_data_from()
Allow cancelling of file operations

Cloning/copying/moving/etc.
Change the way cancellation is handled

Temporary disable raw mode of terminal so that Ctrl-C is be
handled as SIGINT signal rather than as regular input character.

This prevents input characters without any special meaning being
consumed while waiting for cancellation.
Extract main_loop.c::process_scheduled_redraw()

Redraws TUI if it's scheduled.
Extract utils_nix.c:get_proc_exit_status()

Waits for a process to finish and queries for its exit status.
Returns exit status of the process specified by its identifier.
Change cancellation processing rules

* Store and allow querying previous status after disabling
  cancellation processing.
* Add function to reset state (ui_cancellation_reset()).
Move set_sigchld() to utils
Use set_sigchld() in run_in_shell_no_cls()
Consider cmd ec in background_and_wait_for_errors

Previously exit code of a command was completely ignored, only
output to stderr counted.
Fix names of several functions in opt_handlers.c

"prg" part was missing for three functions.
Support cancellation of compound operations

Like removing 1000 files.  Now cancelling one of intermediate
operations will cancel the whole package.
Display information messages about undo/redo

Otherwise it's unclear what is happening after u or ctrl-r.
Extract ui.c:ui_views_reload_visible_filelists()

Extracted from modes/normal.c.

Reloads visible lists of files preserving current position of cursor.