Results of string functions were being converted to decimals by first
  being converted to integers, resulting in a loss of precision.


mysql-test/r/func_str.result:
  Add new results
mysql-test/t/func_str.test:
  Add new regression test
sql/item_strfunc.cc:
  Convert string function results to decimal using string-to-decimal conversion
sql/item_strfunc.h:
  Add Item_str_func::val_decimal()