Uniforming guard characters.

In server-to-client transmissions, responses are separated by a \0x3
character. Now, this is true also in client-to-server direction, replacing
a "\n\n" string.

Therefore, the newline conversion ('\n' character to "\\n" string) in message
body is no longer required.

Moreover, the bug mentioned in 4769b0969e8a86f6a4b2bb3ed54ebd650c5a901f
was actually present in two other functions and is fixed here.