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/common.h

@@ -234,8 +234,8 @@ int mac_read_from_eeprom(void);
 /* common/flash.c */
 void flash_perror (int);
 
-/* common/cmd_autoscript.c */
-int	autoscript (ulong addr, const char *fit_uname);
+/* common/cmd_source.c */
+int	source (ulong addr, const char *fit_uname);
 
 extern ulong load_addr;		/* Default Load Address */