made "test" an ash built-in.

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.