Depending on the queries we use different data processing methods
and can lose some data in case of double (and decimal in 4.1) fields.

The fix consists of two parts:
1. double comparison changed, now double a is equal to double b 
if (a-b) is less than 5*0.1^(1 + max(a->decimals, b->decimals)). 
For example, if a->decimals==1, b->decimals==2, a==b if (a-b)<0.005
2. if we use a temporary table, store double values there as is 
to avoid any data conversion (rounding).


mysql-test/r/type_float.result:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - test result
mysql-test/t/type_float.test:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - test case
sql/field.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - use not_fixed flag instead of dec to check bounds.
sql/field.h:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - Field_Double::not_fixed flag introduced, which is set if dec == NOT_FIXED_DEC
      and is used in the ::store() to check bounds. 
    - new constructor introduced (with not_fixed_arg parameter).
sql/init.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - fill log_01[] array with 0.1 powers.
sql/item_cmpfunc.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - compare_real_fixed() and compare_e_real_fixed() introduced,
      they consider double a == double b if a-b is less than 'precision',
      'precision' is set to 5*0.1^(1 + max(a->decimals, b->decimals)), 
      for example, if a->decimals==1, b->decimals==2, 'precision' is 0.005
    - use the above functions if both arguments are fixed.
sql/item_cmpfunc.h:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - Arg_comparator::presision introduced.
    - Arg_comparator::compare_real_fixed(), Arg_comparator::compare_e_real_fixed() introduced.
sql/mysql_priv.h:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - log_01 array of 0.1 powers added.
sql/mysqld.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - log_01 array of 0.1 powers added.
sql/sql_select.cc:
  fix for bug #19690: ORDER BY eliminates rows from the result
    - if we create double field in a temporary table, set not_fixed flag
      (use proper constructor) to avoid data conversion 
      in the Field_double::store(). Otherwise we can lose some data.