[Ohrrpgce] SVN: teeemcee/7854 multichoice() now makes use of the top half of the screen when the menu

[subversion at HamsterRepublic.com]

teeemcee
2016-03-23 03:32:13 -0700 (Wed, 23 Mar 2016)
400
multichoice() now makes use of the top half of the screen when the menu is long.

Basically, the box+menu gets centred rather than first centering the box and
putting the menu beneath it.

This was absolutely horrible to get right; I should have converted it to slices
instead.

As a bonus, restore vpage when leaving multichoice, so that the screenshot
option in the F8 debug menu works as expected.
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U   wip/common.rbas