when logging is enabled.
Currently the partition engine doesn't allow log tables to
be partitioned. But this was not checked and the server crashed.
Fixed by adding a check in ALTER TABLE to disable partitioning the
log tables.
While working on the cause of the problem improved the way the log
thread structures are initialized before opening the log tables.


mysql-test/r/partition.result:
  Bug #27816: test case
mysql-test/t/partition.test:
  Bug #27816: test case
sql/log.cc:
  Bug #27816: optional
   Improved initialization of the log threads before opening 
   the log table.
   Remedies problems that arise from open_table() et. al. 
   depending on a correctly initialized thd.
   Prerequisite for handling partitioned log tables :
   they call the parser while reading the .frm file.
sql/sql_table.cc:
  Bug #27816: throw an error when paritioning the log tables : 
   not supported by the partition engine.