The old code added to 10.6 was inconsisting in how TCP/IP and
socket connection was chosen. One got also a confusing warning
in some cases.

Examples:
> ../client/mysql --print-defaults
../client/mysql would have been started with the following arguments:
--socket=/tmp/mariadbd.sock --port=3307 --no-auto-rehash
> ../client/mysql
ERROR 2002 (HY000): Can't connect to local server through socket '/tmp/mariadbd.sock' (2)
> ../client/mysql --print-defaults
../client/mysql would have been started with the following arguments:
--socket=/tmp/mariadbd.sock --port=3307 --no-auto-rehash
> ../client/mysql --port=3333
WARNING: Forcing protocol to  TCP  due to option specification. Please explicitly state intended protocol.
ERROR 2002 (HY000): Can't connect to server on 'localhost' (111)
> ../client/mysql --port=3333 --socket=sss
ERROR 2002 (HY000): Can't connect to local server through socket 'sss' (2)
> ../client/mysql --socket=sss --port=3333
ERROR 2002 (HY000): Can't connect to local server through socket 'sss' (2)

Some notable things:
- One gets a warning if one uses just --port if config file sets socket
- Using port and socket gives no warning
- Using socket and then port still uses socket

This patch changes things the following ways:
If --port= is given on the command line, the the protocol is automatically
  changed to "TCP/IP".
- If --socket= is given on the command line, the protocol is automatically
  changed to "socket".
- The last option wins
- No warning is given if protocol changes automatically.