** control artifact to the BLOB table.
*/
static void finish_tag(void){
  Blob record, cksum;
  if( gg.zDate && gg.zTag && gg.zFrom && gg.zUser ){
    blob_zero(&record);
    blob_appendf(&record, "D %s\n", gg.zDate);
    blob_appendf(&record, "T +sym-%F%F%F %s\n", gimport.zTagPre, gg.zTag,
        gimport.zTagSuf, gg.zFrom);
    blob_appendf(&record, "U %F\n", gg.zUser);
    md5sum_blob(&record, &cksum);
    blob_appendf(&record, "Z %b\n", &cksum);
    fast_insert_content(&record, 0, 0, 1);
    blob_reset(&cksum);
  }