The Protocol class has functions for sending values of different types
to the client, one function per type. When sending values that come
from an Item, the function for the corresponding type is called. When
sending a value from a Field, different Protocol functions are called
depending on which protocol is used. If the text protocol is used,
Field::send_text() converts the value to string and calls the Protocol
function that sends a string value to the client. If the binary
protocol is used, Field::send_binary() calls the Protocol function for
the actual type of the value, without converting it to string first.

This causes inconsistencies between the text protocol and the binary
protocol, and also inconsistencies within the text protocol between
values that come from Items and values from Fields.

This patch merges Field::send_text() and Field::send_binary() into a
single function, Field::send_to_protocol(). This function behaves as
the old Field::send_binary() and calls the Protocol function that
corresponds to the value that is to be sent, without converting it to
string first. When the text protocol is used, the value is still
converted to a string, but the conversion happens in the Protocol_text
class.

The Protocol_text class is already capable of converting values to
strings, but it is not aware of the ZEROFILL option of numeric types.
A new zerofill argument was therefore added to the functions for
sending numeric values. The argument is ignored by other protocols
than Protocol_text, as they leave it to the clients to format the
values.

Protocol_text::store(float, ...) used to promote the float argument to
double before converting it to string, which could make the returned
value presented in higher precision than warranted (like
2.299999952316284 instead of 2.3). It is changed to format the float
argument as a float, to be consistent with how it was previously
handled for Fields, and with how the binary protocol handles it.

Field_time_common::send_binary() has code that normalizes hours and
days in the MYSQL_TIME struct. This normalization is only needed by
the binary protocol (in fact, the text protocol does not expect it),
and it is done redundantly in Protocol_binary::store_time(). The code
is removed from Field_time_common, so that it is only performed by
Protocol_binary.

The Protocol_callback class has a flag which controls whether fields
are sent as strings or as native types. This flag is kept, but the
conversion from native types to string is moved into
Protocol_callback::store_field().

Some tests results were changed, mainly because the formatting of
floats resulting from Items changed in the text protocol to match
floats from Fields and floats in general in the binary protocol.

Some test cases which were previously disabled for the binary protocol
because they gave different results on text and binary, have been
enabled, as they now produce the same result with both protocols.

Change-Id: I788a10eb8eb7ec2fe3d4866d0a50dd08c0ac3255