doesn't recognize it
  
This is a 5.1 version of the patch.
  
Problem:
  
'log' and 'log_slow_queries' were "fixed" variables, i.e. they showed up
in SHOW VARIABLES, but could not be used in expressions like 
"select @@log". Also, using them in the SET statement produced an 
incorrect "unknown system variable" error.
  
Solution:

Since as of MySQL 5.1.12 one can enable or disable the general query log
or the slow query log at runtime by changing values of
general_log/slow_query_log, make 'log' and 'log_slow_queries" to be 
synonyms for 'general_log' and 'slow_query_log' respectively.  This 
makes expressions using the '@@var' syntax backward compatible with 
5.0 and SHOW VARIABLES output to be consistent with the SET statement.


mysql-test/r/log_state.result:
  Added a test case for bug #29131.
mysql-test/t/log_state.test:
  Added a test case for bug #29131.
sql/set_var.cc:
  Made the 'log' and 'log_slow_queries' system variables to be synonyms for 'general_log' and 'slow_query_log'.