Prepare to reuse existing pseudo-merge bitmaps by implementing a
`bitmap_equals_ewah()` helper.
This helper will be used to see if a raw bitmap (containing the set of
parents for some pseudo-merge) is equal to any existing pseudo-merge's
commits bitmap (which are stored as EWAH-compressed bitmaps on disk).
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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