spatial index
 While executing OPTIMIZE TABLE on MyISAM tables the server re-creates the
 index file(s) in order to sort them physically by the key. This cannot be 
 done for R-tree indexes as it makes no sense.
 The server was not checking the type of the index and was accessing an 
 R-tree index as if it was a B-tree.
 Fixed by preventing sorting the index file if it contains an R-tree index.  
 


myisam/mi_check.c:
  Bug #23578: Corruption prevents Optimize table from working properly with a
  spatial index
   - disable sorting the index file if it contains an R-tree index.
mysql-test/r/gis-rtree.result:
  Bug #23578: Corruption prevents Optimize table from working properly with a
  spatial index
   - test case
mysql-test/t/gis-rtree.test:
  Bug #23578: Corruption prevents Optimize table from working properly with a
  spatial index
   - test case