Fixes according coercibility tables, p162, SQL Complete


include/my_sys.h:
  Declaration has been moved to /sql directory
sql/item.cc:
  Fixes acording SQL complete, page 162
sql/item_cmpfunc.cc:
  Fixes acording SQL complete, page 162
sql/mysql_priv.h:
  Declaration has been moved here from /include
sql/sql_string.cc:
  A separate variable national_charset_info
sql/sql_yacc.yy:
  A separate variable national_charset_info