many fixes

libmysql/libmysql.c:
  Fixes a very rare bug when variable name (without '_') and it's 
  value are at the very end of the config file.
  
  I have tested it , but would liek little mobster to test it further
mysql-test/r/union.result:
  results for union test that proves that EXPLAIN UNION bugs are fixed
mysql-test/t/union.test:
  additional tests for EXPLAIN on UNION's that have previously failed
sql/sql_yacc.yy:
  Some small fixes for newer parsers.
  Only unsigned int yystacksize remains to be fixed.
  This I leave to Monty.
  Present fixes are only aesthetic and do not harm.

libmysql/libmysql.c

@@ -737,7 +737,7 @@ static void mysql_read_default_options(struct st_mysql_options *options,
 	  *end=0;				/* Remove '=' */
 	}
 	/* Change all '_' in variable name to '-' */
-	for (end= *option ; (end= strcend(end,'_')) ; )
+	for (end= *option ; (end= strcend(end,'_')) && *end ; )
 	  *end= '-';
 	switch (find_type(*option+2,&option_types,2)) {
 	case 1:				/* port */

mysql-test/r/union.result

@@ -86,6 +86,21 @@ explain select a,b from t1 union all select a,b from t2;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ALL	NULL	NULL	NULL	NULL	4	
 t2	ALL	NULL	NULL	NULL	NULL	4	
+explain select xx from t1 union select 1;
+Unknown column 'xx' in 'field list'
+explain select a,b from t1 union select 1;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	ALL	NULL	NULL	NULL	NULL	4	
+				0		0	No tables used
+explain select 1 union select a,b from t1 union select 1;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+				0		0	No tables used
+t1	ALL	NULL	NULL	NULL	NULL	4	
+				0		0	No tables used
+explain select a,b from t1 union select 1 limit 0;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	ALL	NULL	NULL	NULL	NULL	4	
+				0		0	Impossible WHERE
 select a,b from t1 into outfile 'skr' union select a,b from t2;
 Wrong usage of UNION and INTO
 select a,b from t1 order by a union select a,b from t2;

mysql-test/t/union.test

@@ -24,6 +24,12 @@ select 't1',b,count(*) from t1 group by b UNION select 't2',b,count(*) from t2 g
 # Test some error conditions with UNION
 explain select a,b from t1 union all select a,b from t2;
 
+--error  1054
+explain select xx from t1 union select 1;
+explain select a,b from t1 union select 1;
+explain select 1 union select a,b from t1 union select 1;
+explain select a,b from t1 union select 1 limit 0;
+
 --error 1221
 select a,b from t1 into outfile 'skr' union select a,b from t2;
 

sql/sql_yacc.yy

@@ -1928,7 +1928,7 @@ opt_else:
 	| ELSE expr    { $$= $2; }
 
 when_list:
-        { Select->when_list.push_front(new List<Item>) }
+        { Select->when_list.push_front(new List<Item>); }
 	when_list2
 	{ $$= Select->when_list.pop(); }
 
@@ -2031,7 +2031,7 @@ opt_key_definition:
 	  }
 
 key_usage_list:
-	key_or_index { Select->interval_list.empty() } '(' key_usage_list2 ')'
+	key_or_index { Select->interval_list.empty(); } '(' key_usage_list2 ')'
         { $$= &Select->interval_list; }
 
 key_usage_list2:
@@ -2637,7 +2637,7 @@ describe:
 	    YYABORT;
 	}
 	opt_describe_column
-	| describe_command select { Lex->select_lex.options|= SELECT_DESCRIBE };
+	| describe_command select { Lex->select_lex.options|= SELECT_DESCRIBE; }
 
 
 describe_command:
@@ -3077,7 +3077,7 @@ set:
 	  lex->select->select_limit=lex->thd->default_select_limit;
 	  lex->tx_isolation=lex->thd->tx_isolation;
 	  lex->option_type=0;
-	  lex->option_list.empty()
+	  lex->option_list.empty();
 	}
 	option_value_list