Problem: concealed text not revealed when leaving insert mode. (Michael
Soyka)
Solution: Check if concealing changed when leaving insert mode.
(closes#8880)
Problem: Tests using term_wait() can still be flaky.
Solution: Increase the wait time when rerunning a test. (James McCoy,
closes#5899) Halve the initial times to make tests run faster
when there is no rerun.
Problem: Cursor position wrong when resizing and using conceal.
Solution: Set the flags that the cursor position is valid when setting the
row and column during redrawing. (closes#4931)
Problem: Highlighting not updated with conceal and 'cursorline'. (Jason
Franklin)
Solution: Do not use a zero line number. Check if 'conceallevel' is set for
the current window.
