Remove a String parameter from Protocol::store(double/float)

As agreed during a discussion with Monty, let's change the Protocol API from:

virtual bool store(float nr, uint32 decimals, String *buffer);

virtual bool store(double from, uint32 decimals, String *buffer);

to

virtual bool store_float(float nr, uint32 decimals);

virtual bool store_double(double from, uint32 decimals);

I.e.:

• Remove the String* argument
• Rename store(float) and store(double) to store_float() and store_double(), to avoid ambiguity, and to avoid explicit cast in calls.

Rationale to remove the String* argument:

• The String buffer is only needed for Protocol_text. Instead of creating a String buffer on stack for every Field sent, the buffer will go to as a protected member to the class:

  class Protocol_text :public Protocol

  {

  StringBuffer<FLOATING_POINT_BUFFER> buffer;

  public:

  so will be created only once per session. This should give a slight performance improvement.

• It will remove a confusing code, e.g.:

  bool Field_double::send_binary(Protocol *protocol)

  {

  - return protocol->store((double) Field_double::val_real(), dec, (String*) 0);

  + return protocol->store_double(Field_double::val_real(), dec);

  }

  A reader has questions when seeing this code: why a NULL String is passed? when it's important to pass a non-NULL pointer?

• It will make the code more symmetric across various data types.
  Notice, other methods do not have any String buffer parameter:

  virtual bool store_tiny(longlong from);

  virtual bool store_short(longlong from);

  virtual bool store_long(longlong from);

  virtual bool store_longlong(longlong from, bool unsigned_flag);

  virtual bool store_decimal(const my_decimal *);

  virtual bool store_str(const char *from, size_t length,

  CHARSET_INFO *fromcs,

  CHARSET_INFO *tocs);

  virtual bool store(MYSQL_TIME *time, int decimals);

  virtual bool store_date(MYSQL_TIME *time);

  virtual bool store_time(MYSQL_TIME *time, int decimals);