Fix spelling in comments as requested by Osku

This will make charset code easier to understand

include/m_ctype.h

@@ -176,7 +176,7 @@ typedef struct my_charset_handler_st
   uint    (*lengthsp)(struct charset_info_st *, const char *ptr, uint length);
   uint    (*numcells)(struct charset_info_st *, const char *b, const char *e);
   
-  /* Unicode convertion */
+  /* Unicode conversion */
   int (*mb_wc)(struct charset_info_st *cs,my_wc_t *wc,
 	       const unsigned char *s,const unsigned char *e);
   int (*wc_mb)(struct charset_info_st *cs,my_wc_t wc,
@@ -186,7 +186,7 @@ typedef struct my_charset_handler_st
   int (*ctype)(struct charset_info_st *cs, int *ctype,
                const unsigned char *s, const unsigned char *e);
   
-  /* Functions for case and sort convertion */
+  /* Functions for case and sort conversion */
   void    (*caseup_str)(struct charset_info_st *, char *);
   void    (*casedn_str)(struct charset_info_st *, char *);
   uint    (*caseup)(struct charset_info_st *, char *src, uint srclen,
@@ -204,7 +204,7 @@ typedef struct my_charset_handler_st
   
   void (*fill)(struct charset_info_st *, char *to, uint len, int fill);
   
-  /* String-to-number convertion routines */
+  /* String-to-number conversion routines */
   long        (*strntol)(struct charset_info_st *, const char *s, uint l,
 			 int base, char **e, int *err);
   ulong      (*strntoul)(struct charset_info_st *, const char *s, uint l,

mysql-test/t/cast.test

@@ -47,7 +47,7 @@ select cast('1a' as signed);
 select cast('' as signed);
 
 #
-# Character set convertion
+# Character set conversion
 #
 set names binary;
 select cast(_latin1'test' as char character set latin2);

mysql-test/t/query_cache.test

@@ -207,7 +207,7 @@ show status like "Qcache_queries_in_cache";
 drop table t1;
 
 #
-# Charset convertion (cp1251_koi8 always present)
+# Charset conversion (cp1251_koi8 always present)
 #
 create table t1 (a char(1) not null collate koi8r_general_ci);
 insert into t1 values(_koi8r"");

sql/sql_string.cc

@@ -331,7 +331,7 @@ bool String::set_or_copy_aligned(const char *str,uint32 arg_length,
   return copy_aligned(str, arg_length, offset, cs);
 }
 
-	/* Copy with charset convertion */
+	/* Copy with charset conversion */
 
 bool String::copy(const char *str, uint32 arg_length,
 		  CHARSET_INFO *from_cs, CHARSET_INFO *to_cs, uint *errors)

strings/CHARSET_INFO.txt

@@ -172,7 +172,7 @@ mb_wc       - converts the left multibyte sequence into it Unicode code.
 mc_mb       - converts the given Unicode code into multibyte sequence.
 
 
-Case and sort convertion
+Case and sort conversion
 ------------------------
 caseup_str  - converts the given 0-terminated string into the upper case
 casedn_str  - converts the given 0-terminated string into the lower case