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_sequence.h

@@ -80,7 +80,7 @@ protected:
   It's also responsible to generate new values and updating the sequence
   table (engine=SQL_SEQUENCE) trough it's specialized handler interface.
 
-  If increment is 0 then the sequence will be be using
+  If increment is 0 then the sequence will be using
   auto_increment_increment and auto_increment_offset variables, just like
   AUTO_INCREMENT is using.
 */