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_expression_cache.cc

@@ -88,7 +88,7 @@ static uint field_enumerator(uchar *arg)
   @details
   The function creates a temporary table for the expression cache, defines
   the search index and initializes auxiliary search structures used to check
-  whether a given set of of values of the expression parameters is in some
+  whether a given set of values of the expression parameters is in some
   cache entry.
 */