made "test" an ash built-in.

moved the contents of libbb/bb_echo.c back into coreutils/echo.c,
which is a more reasonable place for them than libbb.  this
forces anyone who wants echo and test to be builtin to ash to
also have them available as applets.  their cost is very small,
and the number of people who wouldn't want them as applets is
also very small.

added warning about shell builtins vs. CONFIG_FEATURE_SH_STANDALONE_SHELL,
which conflicts with their use.

thanks to nathanael copa for debugging help.

some string size optimization in test.c may have been lost with
this commit, but this is a good new baseline.

coreutils/Config.in

@@ -603,8 +603,8 @@ config CONFIG_TEST
 	default n
 	help
 	  test is used to check file types and compare values,
-	  returning an appropriate exit code. The shells (ash
-	  and bash) have test builtin.
+	  returning an appropriate exit code.  The bash shell
+	  has test built in, ash can build it in optionally.
 
 config CONFIG_FEATURE_TEST_64
 	bool "Extend test to 64 bit"