* lib/m4sugar/m4sh.m4 (_AS_ECHO_PREPARE): Use a longer test

* lib/m4sugar/m4sh.m4 (_AS_ECHO_PREPARE): Use a longer test
string for more reliable failure.  Wrap the entire test that
causes the broken Solaris printf to dump core, in a subshell,
so the segmentation fault message is reliably suppressed.
Fix shell expansion errors by using /usr/ucb/echo always;
avoid an error on systems without it by another subshell.
Avoid m4 expansion of `$1'.  Set the zeroth argument of the
subshell-$as_echo to `as_echo', for better error message.