transactional SELECT and ALTER TABLE ...  REBUILD PARTITION".

Move declarations of sql_base.cc classes to sql_base.h
(previously declared in sql_class.h).
Became possible after a header file split.





sql/sql_base.cc:
  Make sql_base.h the first include in sql_base.cc.
sql/sql_base.h:
  Add declarations of Prelocking_strategy and Open_table_context.
sql/sql_class.h:
  Remove declarations of Prelocking_strategy and Open_table_context
  (moved).