- Always reset error when calling mysql_stmt_prepare a second time
 - Set stmt->state to MYSQL_STMT_INIT_DONE before closing prepared stmt in server.
 - Add test to mysql_client_test
 - Remove mysql_stmt_close in mysqltest after each query
 - Close all open statements in mysqltest if disable_ps_protocol is called. 


client/mysqltest.c:
  Don't close the statement after each query - reprepare it in next query.
  When "disable_ps_protocol" is issued make sure to close all open
  statements. Otherwise the test for @@max_prepared_statements fails. But we
  also get a test that the statements that are open can be closed and reopened
  in the middle of the tests.
libmysql/libmysql.c:
  Reset the last error every time mysql_stmt_prepare is called.
  Set state to MYSQL_STMT_INIT_DONE befoe closing it in the server. That way
  we will always have right status regardless of wheter close fails or not.
tests/mysql_client_test.c:
  Add testcase for bug15518, re-prepare a previously prepare statement that has failed
  to prepare. Test also when connection to server has been lost inbetween.
  Change all assert to DIE_UNLESS so we get printout of line and an error message
  if it fails.