[Ohrrpgce] SVN: teeemcee/9845 Convert show_help to use a scroll slice and new-style text slice

[subversion at HamsterRepublic.com]

teeemcee
2017-12-03 04:47:56 -0800 (Sun, 03 Dec 2017)
430
Convert show_help to use a scroll slice and new-style text slice

Instead of using first_line or line_limit (which aren't supported by
wrapprint-based text slices), the text slice is scrolled up and down.
However, still switches the text slice back to old-style wrapping when
editing, so that the cursor is drawn correctly.

Incidentally this results in more CPU usage when editing, and less when viewing.

(Ported from wip r9836)
---
U   rel/etheldreme/common.rbas
U   rel/etheldreme/slices.bas