pack-bitmap: implement bitmap_writer_has_bitmapped_object_id()

Prepare to implement pseudo-merge bitmap selection by implementing a
necessary new function, `bitmap_writer_has_bitmapped_object_id()`.

This function returns whether or not the bitmap_writer selected the
given object ID for bitmapping. This will allow the pseudo-merge
machinery to reject candidates for pseudo-merges if they have already
been selected as an ordinary bitmap tip.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pack-bitmap-write.c

@@ -130,6 +130,12 @@ void bitmap_writer_build_type_index(struct bitmap_writer *writer,
 	}
 }
 
+int bitmap_writer_has_bitmapped_object_id(struct bitmap_writer *writer,
+					  const struct object_id *oid)
+{
+	return kh_get_oid_map(writer->bitmaps, *oid) != kh_end(writer->bitmaps);
+}
+
 /**
  * Compute the actual bitmaps
  */