prepared statements."


include/hash.h:
  New declaration for hash_reset() function. The old version was not used.
libmysql/client_settings.h:
  Declaration for mysql_detach_stmt_list().
libmysql/libmysql.c:
  Fix for bug#5315 "mysql_change_user() doesn't free prepared statements":
  add call to mysql_detach_stmt_list(prepared statements) to
  mysql_change_user(): all statements are freed by server, so client
  counterparts need to be marked as not usable.
mysys/hash.c:
  Fix for bug#5315 "mysql_change_user() doesn't free prepared statements":
  implementation of hash_reset(), which frees all hash elements
  and prepares the hash for reuse.
sql-common/client.c:
  Fix for bug#5315 "mysql_change_user() doesn't free prepared statements":
  implementation of mysql_detach_stmt_list(): zero connection pointer
  in given statement list, thus marking given statements as not usable.
sql/sql_class.cc:
  Fix for bug#5315 "mysql_change_user() doesn't free prepared statements":
  reset prepared statements map in THD::change_user().
sql/sql_class.h:
  Fix for bug#5315 "mysql_change_user() doesn't free prepared statements":
  implementation of Statement_map::reset().
  A little cleanup of ~Statement_map(): first empty names_hash, as st_hash
  has a free function, which will delete statements.
tests/client_test.c:
  A test case for bug #5315 "mysql_change_user() doesn't free prepared
  statements".