Problem: setting/displaying @@LC_TIME_NAMES didn't distinguish between
GLOBAL and SESSION variable types - always SESSION variable
was set/shonw.
Fix: set either global or session value.
Also, "mysqld --lc-time-names" was added to set "global default" value.


mysql-test/r/variables.result:
  Adding test cases
mysql-test/t/variables.test:
  Adding test cases
sql/mysql_priv.h:
  Declaring variable for global default.
sql/mysqld.cc:
  Adding --lc-time-names
sql/set_var.cc:
  Distinguish between GLOBAL and SESSION variables.
sql/sql_class.cc:
  Don't initialize to en_US, use global_system_variables value instead.