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/keymile-common.h b/include/configs/keymile-common.h
index 58b95f4..b2e37ec 100644
--- a/include/configs/keymile-common.h
+++ b/include/configs/keymile-common.h
@@ -240,7 +240,7 @@
 		"new_esw_0x${IVM_BoardId}_0x${IVM_HWKey}.scr \0"	\
 	"new_esw=run set_new_esw_script; "				\
 		"tftp ${autoscr_ws} ${new_esw_script}; "		\
-		"iminfo ${autoscr_ws}; autoscr ${autoscr_ws} \0"	\
+		"iminfo ${autoscr_ws}; source ${autoscr_ws} \0"	\
 	"bootlimit=0 \0" 						\
 	CONFIG_KM_DEF_ENV_IOMUX						\
 	CONFIG_KM_DEF_ENV_PRIVATE					\