Extract is_file_name_changed() function in fileops

To make code more readable.
Add ST_NONE error signalling type
Use ST_NONE instead of ST_STATUS_BAR in tests

TUI is not initialized in tests, so this is more correct way of doing
testing.
Fix displaying of false error messages rename

Function which performs the check was told to display errors to a user,
but it wasn't needed as solely results of the function were needed.
Merge branch 'remove-false-error-messages-on-rename'

Fix displaying of barely visible false error messages on the status
bar on some rename operations.