Fix redrawing issues with narrow screen and remove extra wait in resize tests

Before this, bottom of screen got messed up when modemsg (+ one extra
space to not force terminal scroll) didn't fit on one line.

Saves ~10 seconds in UI tests

closes #8466
closes #8664
Regression by 0d7daaad98d5.

- Fix length comparison.
- Fix loop(s) which iterated over all fields of array `pcc` even if it
  was not filled up (try unicode 0x9f as statusline character).

Note about the tests:
- To input unicode with more than two hex digits you can use <C-v>U...:
  a + U+fe20: a︠
  a + U+fe20 + U+fe21: a︠︡

closes #7383
closes #7715

This implements the compromise described in #7383:
* low-priority CursorLine if foreground is not set
* high-priority ("same as Vim" priority) CursorLine if foreground is set

ref d1874ab2821d076397290cc154d87ec2dc352c79
ref 56eda2aa17c80ba380b606f9466f288fb8162dd3

Because we default to laststatus=2 (statusline is always visible), the
:edit message is not useful.

ref #6289

Problem:    For some people the hint about quitting is not sufficient.
Solution:   Put <Enter> separately.  Also use ":qa!" to get out even when
            there are changes.
https://github.com/vim/vim/commit/28a8193e3113f676f89fb6312b099d849df881d3

According to POSIX[0], only octal escapes are supported by the printf
command.  GNU coreutils' printf and some shells' builtin printf versions
which support hex escapes, but dash and non-GNU printf do not.

[0]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/printf.html