Added "SHOW AUTHORS" code

mysql-test/r/show_check.result:
  Update to results
mysql-test/t/show_check.test:
  Added SHOW AUTHORS test
sql/field.h:
  Fixed portability issue
sql/lex.h:
  Added new keyword "AUTHORS"
sql/mysql_priv.h:
  Added reference to new show command.
sql/sql_cache.h:
  Fixed compile bug (more of these need to be fixed)
sql/sql_lex.h:
  Added to com bit.
sql/sql_parse.cc:
  Parsing for show authors
sql/sql_show.cc:
  Added new show command for "SHOW AUTHORS"
sql/sql_yacc.yy:
  Added new parse code for show authors.

sql/sql_lex.h

@@ -92,6 +92,7 @@ enum enum_sql_command {
   SQLCOM_XA_START, SQLCOM_XA_END, SQLCOM_XA_PREPARE,
   SQLCOM_XA_COMMIT, SQLCOM_XA_ROLLBACK, SQLCOM_XA_RECOVER,
   SQLCOM_INSTALL_PLUGIN, SQLCOM_UNINSTALL_PLUGIN,
+  SQLCOM_SHOW_AUTHORS,
   /* This should be the last !!! */
 
   SQLCOM_END