Adds --general-log-file, --slow-query-log-file command-
line options to match system variables of the same names.

Deprecates --log, --log-slow-queries command-line option
and log, log_slow_queries system-variables for v7.0; they
are superseded by general_log/general_log_file and
slow_query_log/slow_query_log_file, respectively.

mysql-test/r/log_basic.result:
  Change deprecated system variable "log" to
  general log.
mysql-test/r/log_bin_trust_routine_creators_basic.result:
  Change deprecation warning so it's more obvious we're referring
  to a variable.
mysql-test/r/log_state.result:
  Show that all log-related server variables that
  should throw deprecation warnings do, and the
  others don't.
mysql-test/r/warnings.result:
  Change deprecation warning so it's more obvious we're referring
  to a variable.
mysql-test/suite/rpl/r/rpl_sp.result:
  Change deprecation warning so it's more obvious we're referring
  to a variable.
mysql-test/t/log_basic.test:
  Change deprecated system variable "log" to
  general log.
mysql-test/t/log_state.test:
  Show that all log-related server variables that
  should throw deprecation warnings do, and the
  others don't.
sql/mysqld.cc:
  Add command-line options --general-log-file and
  --slow-query-log-file to match server options of
  the same name.
  
  Deprecated --log and --log-slow-queries command-line
  options; they are superseded by --general-log/
  --general-log-file and --slow-query-log/--slow-query-log-file,
  respectively
sql/set_var.cc:
  Deprecate system-variables log in favour of general_log,
  log_slow_queries in favour of slow_query_log for 7.0,
  both for value- and DEFAULT-setting.