Fixed that MyISAM were not working properly with non-8bit charsets in some cases
CONVERT() function now works properly


myisam/mi_unique.c:
  Fix for non-8bit charsets
sql/field.cc:
  Initialize blobs with charset
sql/field.h:
  Initialize blobs with charset
sql/field_conv.cc:
  Initialize blobs with charset
sql/item_strfunc.cc:
  CONVERT() function now has working fix_lenght_and_dec(), and it's own 
  fix_fields()
sql/item_strfunc.h:
  CONVERT() function now has working fix_lenght_and_dec(), and it's own 
  fix_fields()
sql/sql_select.cc:
  Fixes for BLOBs
  Fixed that wrong charset was used in some cases