Add "source" command; prepare removal of "autoscr" command

According to the doc/feature-removal-schedule.txt, the "autoscr"
command will be replaced by the "source" command in approximately 6
months from now.

This patch prepares this change and starts a 6 month transition
period as follows:

- The new "source" command has been added, which implements exactly
  the same functionlaity as the old "autoscr" command before
- The old "autoscr" command name is kept as an alias for compatibility
- Command sequences, script files atc. have been adapted to use the
  new "source" command
- Related environment variables ("autoscript", "autoscript_uname")
  have *not* been adapted yet; these will be renamed resp. removed in
  a separate patch when the support for the "autoscr" command get's
  finally dropped.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/configs/NX823.h b/include/configs/NX823.h
index 9182223..5054d5e 100644
--- a/include/configs/NX823.h
+++ b/include/configs/NX823.h
@@ -55,7 +55,7 @@
 #define CONFIG_LOADS_ECHO	1	/* echo on for serial download	*/
 #undef	CONFIG_SYS_LOADS_BAUD_CHANGE		/* don't allow baudrate change	*/
 #undef	CONFIG_WATCHDOG			/* watchdog disabled, for now	    */
-#define CONFIG_AUTOSCRIPT
+#define CONFIG_SOURCE
 
 /*
  * BOOTP options
@@ -72,7 +72,7 @@
  */
 #include <config_cmd_default.h>
 
-#define CONFIG_CMD_AUTOSCRIPT
+#define CONFIG_CMD_SOURCE
 
 
 /* call various generic functions */