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/README b/README
index 32d9acd..fcc4d7c 100644
--- a/README
+++ b/README
@@ -593,7 +593,6 @@
 		except those marked below with a "*".
 
 		CONFIG_CMD_ASKENV	* ask for env variable
-		CONFIG_CMD_AUTOSCRIPT	  Autoscript Support
 		CONFIG_CMD_BDI		  bdinfo
 		CONFIG_CMD_BEDBUG	* Include BedBug Debugger
 		CONFIG_CMD_BMP		* BMP support
@@ -654,6 +653,7 @@
 					  (requires CONFIG_CMD_I2C)
 		CONFIG_CMD_SETGETDCR	  Support for DCR Register access
 					  (4xx only)
+		CONFIG_CMD_SOURCE	  "source" command Support
 		CONFIG_CMD_SPI		* SPI serial bus support
 		CONFIG_CMD_USB		* USB support
 		CONFIG_CMD_VFD		* VFD support (TRAB)
@@ -1789,7 +1789,7 @@
 
 		Note: overly (ab)use of the default environment is
 		discouraged. Make sure to check other ways to preset
-		the environment like the autoscript function or the
+		the environment like the "source" command or the
 		boot command first.
 
 - DataFlash Support:
@@ -1948,8 +1948,8 @@
    81	common/cmd_net.c	NetLoop() back without error
   -82	common/cmd_net.c	size == 0 (File with size 0 loaded)
    82	common/cmd_net.c	trying automatic boot
-   83	common/cmd_net.c	running autoscript
-  -83	common/cmd_net.c	some error in automatic boot or autoscript
+   83	common/cmd_net.c	running "source" command
+  -83	common/cmd_net.c	some error in automatic boot or "source" command
    84	common/cmd_net.c	end without errors
 
 FIT uImage format:
@@ -2952,7 +2952,7 @@
   autoscript	- if set to "yes" commands like "loadb", "loady",
 		  "bootp", "tftpb", "rarpboot" and "nfs" will attempt
 		  to automatically run script images (by internally
-		  calling "autoscript").
+		  calling "source").
 
   autoscript_uname - if script image is in a format (FIT) this
 		     variable is used to get script subimage unit name.