- Add funtion "query_get_value to allow reading a fields value
   into a $variable


client/mysqltest.c:
  - Add function "let $var= query_get_value(<query>,<colname>,<row>)"
    making it possible to read a value from a specific field in a query 
    into a $variable.
mysql-test/r/mysqltest.result:
  Add test cases for "query_get_value"
mysql-test/t/mysqltest.test:
  Add test cases for "query_get_value"