Add halt, halt_error builtins (fix #386)

tests/setup

@@ -15,9 +15,11 @@ JQ=$JQBASEDIR/jq
 if [ -z "${NO_VALGRIND-}" ] && which valgrind > /dev/null; then
     VALGRIND="valgrind --error-exitcode=1 --leak-check=full \
                        --suppressions=$JQTESTDIR/onig.supp"
+    VG_EXIT0=--error-exitcode=0
     Q=-q
 else
     VALGRIND=
+    VG_EXIT0=
     Q=
 fi