This avoids having to delete the device context and the bitmap selected
into it just to update the bitmap, since it was setting preview.hdc to
NULL to indicate that these bitmaps needed to be updated. This patch
also helps make WM_PAINT messages get processed faster by moving this out
of the code for handling WM_PAINT.

Previously hdc2 needed to be deleted and set to NULL to indicate that only
one page should be shown. I have avoided this using a new variable for
the preview structure.

The device context were also being deleted without deleting the bitmaps
created for them and selected into them, so this patch also gets these
bitmaps and deletes them with their device context.

Rather than making seperate calls to EM_FORMATRANGE to get the number of
pages and the character boundaries, it would be easiest to get both
together.  The time to process EM_FORMATRANGE seems like it would take a
lot longer than the time needed to cache the character page boundaries.

The existing tests were not properly testing the return value for the case
where all the text fits in the page rect, so this patch adds a couple of
simple tests for this case.

winex11: When a mask picture is active, the source offsets should be relative to mask_pict instead of src_pict.

For a Mac user in Australia, for example, the out-of-the-box configuration is
that the preferred language is generic English ("en").  Their formats locale
should be Australia ("en_AU").  Detect that case and don't override
LC_MESSAGES.

This enables it to be auto-updated by make_makefiles.