(x_produce_image_glyph, x_append_stretch_glyph): Accomodate to changes in struct glyph starting 1999-12-27. Some bit-fields of struct glyph were not set, which made glyphs unequal when compared with GLYPH_EQUAL_P. Redisplay outputs such glyphs, and flickering effects were the result. This also depended on the contents of memory returned by xmalloc. If flickering happens again, activate the code in clear_glyph_row that's in #if 0. If the flickering is gone with that, chances are that it is caused by something similar.
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