Revenge of the $ECHO. Kill most uses of Xsed.

Revenge of the $ECHO. Kill most uses of Xsed.

* libltdl/config/general.m4sh: Replace all uses of `$ECHO "X..."
| $Xsed' with `$ECHO "..." | $SED', and employ further trivial
simplifications.  Replace $ECHO with echo where appropriate.
(func_echo_all): New function.
* libltdl/config/getopt.m4sh: Likewise simplifications.
* libltdl/config/ltmain.m4sh: Likewise.
* libltdl/m4/libtool.m4: Likewise.
(LT_CMD_MAX_LEN): Use func_fallback_echo, to ensure that the
command line is passed through an exec* function.
* libtoolize.m4sh: Likewise simplifications.  Use func_echo_all
to implement --dry-run.
* tests/defs.m4sh: Likewise simplifications.
* tests/quote.test: Likewise simplifications.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>