WL#5796: Move definition of replication server variables to library

This is a step towards making replication a library, such that the 5.6 rpl-lib can  
be plugged into the 5.5 core [WL#5675].

We move all server variables defined by replication from core to rpl-lib. Each 
server variable will be defined in the init() function of one of the classes 
Binlog, Master, and Slave.

The following variables should be moved from core to rpl-lib (the names listed 
here are the internal names used in sys_vars.cc, they may differ from the names of 
the command line options and system variables).

binlog_cache_size
binlog_stmt_cache_size
max_binlog_size
max_relaylog_size
binlog_checksum
report_[host|user|password|port]
log_slave_updates
relay_logname
relay_log_index
log_bin_index
relay_log_basename
log_bin_basename
relay_log_info_filename
slave_load_tmpdir
slave_net_timeout
slave_skip_counter
slave_skip_errors
relay_log_space_limit