hush: wait for `cmd` to complete, and immediately store its exitcode in $?

function                                             old     new   delta
expand_vars_to_list                                 2129    2197     +68

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush_test/hush-psubst/tick5.tests b/shell/hush_test/hush-psubst/tick5.tests
new file mode 100755
index 0000000..bd160c9
--- /dev/null
+++ b/shell/hush_test/hush-psubst/tick5.tests
@@ -0,0 +1 @@
+true; echo `false` $?