cleanup frm creation:

* comments
* cosmetic changes, *(ptr+5) -> ptr[5]
* a couple of trivial functions -> inline
* remove unused argument from pack_header()
* create_frm() no longer creates frm file (the function used to prepare and
  fill a memory buffer and call my_create at the end. Now it only prepares
  a memory buffer). Renamed accordingly.
* don't call pack_screen twice, go for a smaller screen area in the first attempt
* remove useless calls to check_duplicate_warning()
* don't write unireg screens to .frm files
* remove make_new_entry(), it's basically dead code, always calculating
  and writing into frm the same string value. replace the function call
  with the constant string.

sql/unireg.h

@@ -179,6 +179,9 @@ int rea_create_table(THD *thd, const char *path,
                      uint key_count,KEY *key_info,
                      handler *file);
 
+#define FRM_HEADER_SIZE 64
+#define FRM_FORMINFO_SIZE 288
+
 static inline bool is_binary_frm_header(uchar *head)
 {
   return head[0] == 254