Bug #25097 mysql_server_init fails silently if no errmsg.sys is present.

There was no way to return an error from the client library
if no MYSQL connections was established.
So here i added variables to store that king of errors and
made functions like mysql_error(NULL) to return these.


client/mysql.cc:
  Bug #25097 mysql_server_init fails silently if no errmsg.sys is present.
  
  Show the error message on std_error
include/sql_common.h:
  Bug #25097 mysql_server_init fails silently if no errmsg.sys is present.
  
  cant_connect_sqlstate constant declared
libmysql/libmysql.c:
  Bug #25097 mysql_server_init fails silently if no errmsg.sys is present.
  
  mysql_sqlstate(NULL) returns 'unknown_sqlstate'
libmysqld/lib_sql.cc:
  Bug #25097 mysql_server_init fails silently if no errmsg.sys is present.
  
  EMBEDDED_SERVER version of the vprint_msg_to_log() implemented
sql-common/client.c:
  Bug #25097 mysql_server_init fails silently if no errmsg.sys is present.
  
  mysql_server_last_errno and mysql_server_last_error introduced
  to store errors not related to particular connections.
  
  mysql_error(NULL) and mysql_errno(NULL) now returns these
  mysql_server_last_error and errno respectively
sql/log.cc:
  Bug #25097 mysql_server_init fails silently if no errmsg.sys is present.
  
  EMBEDDED_LIBRARY implementation of the vprint_msg_to_log() moved
  to lib_sql.cc

include/sql_common.h

@@ -15,6 +15,7 @@
 
 
 extern const char	*unknown_sqlstate;
+extern const char	*cant_connect_sqlstate;
 extern const char	*not_error_sqlstate;
 
 #ifdef	__cplusplus