This reduces the amount of flicker seen from redrawing the window.

This extra buffer only saves the result of the StretchBlt operatation,
which isn't worth doing since a BitBlt will still be needed from the buffer
to the screen. This causes noticable delay on resizing since a new sized
bitmap needs to be created, the old bitmap needs to be destroyed, and then
both a StretchBlt and a Bitblt is needed to actually repaint the window.

If there is a selection that doesn't span multiple paragraphs, then the
selection text initializes the find field in native wordpad, otherwise the
last search is used to initialize the field.  I added an extra buffer,
since closing the find dialog before doing a search will preserve the last
search state.

Pressing replace should only replace a selected match, and afterwards it
should find the next match. Searches should always start from the start of
the selection, even if the selection is moved in between searches. Searches
wrap at the end of text, and should keep track of whether it has wrapped
from previous searches to determine if it reached the end position.

The few functions that care about the read buffer should explicitly set it
themselves, instead of assuming any particular state.

Note how both ddraw 1 and ddraw 7 used the same IDirectDrawImpl_XXX naming
convention.