reset mysql->net.last_error": the solution is to clear
MYSQL->net error before performing COM_CLOSE: if the call
succeeds, the connection is usable for other statements.
More comprehensive fix is to clear MYSQL->net for all
recoverable errors at the time they happen, it will be
implemented in 5.0 as it introduces incompatibility in behavior.


libmysql/libmysql.c:
  A simple fix for Bug#7990 "mysql_stmt_close doesn't reset 
  mysql->net.last_error"
tests/mysql_client_test.c:
  A test case for Bug#7990 " mysql_stmt_close doesn't reset 
  mysql->net.last_error"