Cache parameters print added in EXPLAIN EXTENDED output.

mysql-test/r/compare.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/group_by.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect3.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect3_jcl6.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect4.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect_cache.result:
  Added test suite for LP BUG#615760
mysql-test/r/subselect_mat.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect_no_mat.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect_no_opts.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect_no_semijoin.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect_sj.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/r/subselect_sj_jcl6.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/suite/pbxt/r/subselect.result:
  Cache parameters print added in EXPLAIN EXTENDED output.
mysql-test/t/subselect_cache.test:
  Cache parameters print added in EXPLAIN EXTENDED output.
sql/item.cc:
  Item::set_expr_cache result fixed according to its description.
  
  Cache parameters print added in EXPLAIN EXTENDED output.
sql/item.h:
  Cache parameters print added in EXPLAIN EXTENDED output.
sql/item_cmpfunc.cc:
  Check on double cache assignment added into the transformation methods.
sql/item_cmpfunc.h:
  Check on double cache assignment added into the transformation methods.
sql/item_subselect.cc:
  Check on double cache assignment added into the transformation methods.
sql/item_subselect.h:
  Check on double cache assignment added into the transformation methods.
sql/sql_expression_cache.cc:
  Cache parameters print added.
sql/sql_expression_cache.h:
  Cache parameters print added.
sql/sql_select.cc:
  Removed unused method (now it is impossible to make double transformation with the cache).
sql/sql_select.h:
  Removed unused method.