WL#1249: SHOW VARIABLES to show both server-side and client-side values

Affects: Server-7.1   —   Status: Un-Assigned   —   Priority: Medium

Some "server" variables like max_join_size and max_allowed_packet are 
specified on both the server side and the client side. Currently, the default 
values are (v. 4.1.0): 
Value       max_allowed_packet   max_join_size 
Client             16777216            1000000 
Server              1048576         4294967295 
The problem that is addressed by this worklog entry: It's impossible to tell 
from the client side (a) what is the actual value being used on the current 
conncetion, and (b) how did the server/client negotiate this value. The only 
manner in which we can get these values while connected are through SHOW 
VARIABLES, and this only provides us with the server values. 
1) Keep the current variable names, but change the semantics to reflect the 
*actual* values in use over the current connection 
2) introduce two new variables per existing variables, e.g. 
max_allowed_packet_server and max_allowed_packet_client, which will contain 
the values as defined by the server and client respectively.