Problems:
- dot character was always printed as decimal point
  instead of localized decimal point for short
  numbers without thousands
- Item_func_format::val_str always returned values in ASCII
format,
  regargless of @@character_set_connection, which in case of utf32
  led to crash in debug build, or to incorrect values in release build.

Fix:
- Adding a piece of code to replace dot character to
  localized decimal point in short numbers.
- Changing parent class for Item_func_format to
  Item_str_ascii_func, because its val_str() implementation is heavily ASCII oriented.