Feature Removal: disable "mtest" command by default

The "mtest" command is of little practical use (if any), and
experience has shown that a large number of board configurations
define useless or even dangerous start and end addresses.  If not even
the board maintainers are able to figure out which memory range can be
reliably tested, how can we expect such from the end users?  As this
problem comes up repeatedly, we rather do not enable this command by
default, so only people who know what they are doing will be
confronted with it.

As this changes the user interface, we allow for a grace period
before this change takes effect. For now, we make "mtest"
configurable through the CONFIG_CMD_MEMTEST variable, which is defined
in include/config_cmd_default.h;  we also add an entry to
doc/feature-removal-schedule.txt which announces the removal of this
default setting in two releases from now, i. e. with v2013.07.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Tom Rini <trini@ti.com>
diff --git a/README b/README
index 42544ce..869694f 100644
--- a/README
+++ b/README
@@ -860,7 +860,8 @@
 					  (requires CONFIG_CMD_MEMORY and CONFIG_MD5)
 		CONFIG_CMD_MEMINFO	* Display detailed memory information
 		CONFIG_CMD_MEMORY	  md, mm, nm, mw, cp, cmp, crc, base,
-					  loop, loopw, mtest
+					  loop, loopw
+		CONFIG_CMD_MEMTEST	  mtest
 		CONFIG_CMD_MISC		  Misc functions like sleep etc
 		CONFIG_CMD_MMC		* MMC memory mapped support
 		CONFIG_CMD_MII		* MII utility commands