Fixed typos

- Removed duplicate words, like "the the" and "to to"
- Removed duplicate lines (one double sort line found in mysql.cc)
- Fixed some typos found while searching for duplicate words.

Command used to find duplicate words:
egrep -rI "\s([a-zA-Z]+)\s+\1\s" | grep -v param

Thanks to Artjoms Rimdjonoks for the command and pointing out the
spelling errors.

sql/sql_class.h

@@ -6690,7 +6690,7 @@ public:
     ("c"),("b"),("c"),("c"),("a"),("b"),("g")
     ("c"),("a"),("b"),("d"),("b"),("e")
 
-  - Let's demonstrate how the the set operation INTERSECT ALL is proceesed
+  - Let's demonstrate how the set operation INTERSECT ALL is proceesed
     for the query
               SELECT f FROM t1 INTERSECT ALL SELECT f FROM t2
 
@@ -6738,7 +6738,7 @@ public:
       |0      |1      |c  |
       |0      |1      |c  |
 
-  - Let's demonstrate how the the set operation EXCEPT ALL is proceesed
+  - Let's demonstrate how the set operation EXCEPT ALL is proceesed
     for the query
               SELECT f FROM t1 EXCEPT ALL SELECT f FROM t3
 
@@ -7341,7 +7341,7 @@ class multi_update :public select_result_interceptor
 {
   TABLE_LIST *all_tables; /* query/update command tables */
   List<TABLE_LIST> *leaves;     /* list of leaves of join table tree */
-  List<TABLE_LIST> updated_leaves;  /* list of of updated leaves */
+  List<TABLE_LIST> updated_leaves;  /* list of updated leaves */
   TABLE_LIST *update_tables;
   TABLE **tmp_tables, *main_table, *table_to_update;
   TMP_TABLE_PARAM *tmp_table_param;