Correcting signature for my_strndup to be able to build on Windows

in pushbuild on Replication/Backup team tree.

include/my_sys.h

@@ -163,7 +163,7 @@ extern gptr my_realloc(gptr oldpoint,uint Size,myf MyFlags);
 extern void my_no_flags_free(gptr ptr);
 extern gptr my_memdup(const byte *from,uint length,myf MyFlags);
 extern char *my_strdup(const char *from,myf MyFlags);
-extern char *my_strndup(const byte *from, uint length,
+extern char *my_strndup(const char *from, uint length,
 				   myf MyFlags);
 /* we do use FG (as a no-op) in below so that a typo on FG is caught */
 #define my_free(PTR,FG) ((void)FG,my_no_flags_free(PTR))
@@ -587,7 +587,7 @@ extern gptr _my_memdup(const byte *from,uint length,
 		       const char *sFile, uint uLine,myf MyFlag);
 extern my_string _my_strdup(const char *from, const char *sFile, uint uLine,
 			    myf MyFlag);
-extern char *_my_strndup(const byte *from, uint length,
+extern char *_my_strndup(const char *from, uint length,
 				    const char *sFile, uint uLine,
 				    myf MyFlag);
 

mysys/safemalloc.c

@@ -525,7 +525,7 @@ char *_my_strdup(const char *from, const char *filename, uint lineno,
 } /* _my_strdup */
 
 
-char *_my_strndup(const byte *from, uint length,
+char *_my_strndup(const char *from, uint length,
 			     const char *filename, uint lineno,
 			     myf MyFlags)
 {