Bug #26794:

Different set of conditions is used to verify
the validity of index definitions over a GEOMETRY
column in ALTER TABLE and CREATE TABLE. 
The difference was on how sub-keys notion validity
is checked.
Fixed by extending the CREATE TABLE condition to
support the cases allowed in ALTER TABLE.
Made the SHOW CREATE TABLE not to display spatial
indexes using the sub-key notion.

sql/field.cc

@@ -1011,6 +1011,7 @@ bool Field::type_can_have_key_part(enum enum_field_types type)
   case MYSQL_TYPE_BLOB:
   case MYSQL_TYPE_VAR_STRING:
   case MYSQL_TYPE_STRING:
+  case MYSQL_TYPE_GEOMETRY:
     return TRUE;
   default:
     return FALSE;