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>

include/configs/NETTA2.h

@@ -71,7 +71,7 @@
 	"ip=${ipaddr}:${serverip}:${gatewayip}:${netmask}:${hostname}::off; "	\
 	"bootm"
 
-#define CONFIG_AUTOSCRIPT
+#define CONFIG_SOURCE
 #define CONFIG_LOADS_ECHO	0	/* echo off for serial download	*/
 #undef	CONFIG_SYS_LOADS_BAUD_CHANGE		/* don't allow baudrate change	*/