causing crashes!

Adding a SPATIAL INDEX on a non-geometrical column caused a
segmentation fault when the table was subsequently 
inserted into.
      
A test was added in mysql_prepare_create_table to explicitly
check whether non-geometrical columns are used in a
spatial index, and throw an error if so.


mysql-test/t/gis.test:
  Added test cases to verify that only geometrical
  columns can get a spatial index.
          
  In addition, verify that only a single geom.
  column can participate in a spatial index.