MEDIUM: config: reject conflicts in table names

MEDIUM: config: reject conflicts in table names

A nasty situation happens when two tables have the same name. Since it
is possible to declare a table in a frontend and another one in a backend,
this situation may happen and result in a random behaviour each time a
table is designated in a "stick" or "track" rule. Let's make sure this
is properly detected and stopped. Such a config will now report :

[ALERT] 145/104933 (31571) : parsing [prx.cfg:36] : stick-table name 't' conflicts with table declared in frontend 't' at prx.cfg:30.
[ALERT] 145/104933 (31571) : Error(s) found in configuration file : prx.cfg
[ALERT] 145/104933 (31571) : Fatal errors found in configuration.