Auto-merge from mysql-trunk-bugfixing.

******
This patch fixes the following bugs:
  - Bug#5889: Exit handler for a warning doesn't hide the warning in
    trigger
  - Bug#9857: Stored procedures: handler for sqlwarning ignored
  - Bug#23032: Handlers declared in a SP do not handle warnings generated
    in sub-SP
  - Bug#36185: Incorrect precedence for warning and exception handlers

The problem was in the way warnings/errors during stored routine execution
were handled. Prior to this patch the logic was as follows:

  - when a warning/an error happens: if we're executing a stored routine,
    and there is a handler for that warning/error, remember the handler,
    ignore the warning/error and continue execution.

  - after a stored routine instruction is executed: check for a remembered
    handler and activate one (if any).

This logic caused several problems:

  - if one instruction generates several warnings (errors) it's impossible
    to choose the right handler -- a handler for the first generated
    condition was chosen and remembered for activation.

  - mess with handling conditions in scopes different from the current one.

  - not putting generated warnings/errors into Warning Info (Diagnostic
    Area) is against The Standard.

The patch changes the logic as follows:

  - Diagnostic Area is cleared on the beginning of each statement that
    either is able to generate warnings, or is able to work with tables.

  - at the end of a stored routine instruction, Diagnostic Area is left
    intact.

  - Diagnostic Area is checked after each stored routine instruction. If
    an instruction generates several condition, it's now possible to take a
    look at all of them and determine an appropriate handler.

sql/sql_class.h

@@ -2800,23 +2800,6 @@ private:
                   MYSQL_ERROR::enum_warning_level level,
                   const char* msg);
 
-  /**
-    Raise a generic SQL condition, without activation any SQL condition
-    handlers.
-    This method is necessary to support the RESIGNAL statement,
-    which is allowed to bypass SQL exception handlers.
-    @param sql_errno the condition error number
-    @param sqlstate the condition SQLSTATE
-    @param level the condition level
-    @param msg the condition message text
-    @return The condition raised, or NULL
-  */
-  MYSQL_ERROR*
-  raise_condition_no_handler(uint sql_errno,
-                             const char* sqlstate,
-                             MYSQL_ERROR::enum_warning_level level,
-                             const char* msg);
-
 public:
   /** Overloaded to guard query/query_length fields */
   virtual void set_statement(Statement *stmt);