hush: support $_NUMBERS variable names

diff --git a/shell/hush_test/hush-vars/var2.tests b/shell/hush_test/hush-vars/var2.tests
new file mode 100755
index 0000000..1292410
--- /dev/null
+++ b/shell/hush_test/hush-vars/var2.tests
@@ -0,0 +1,4 @@
+_1=http://busybox.net
+
+echo $_1
+echo ${_1}_abc