ash: add all hush parsing tests to ast tests

All pass.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash_test/ash-parsing/quote4.tests b/shell/ash_test/ash-parsing/quote4.tests
new file mode 100755
index 0000000..f1dabfa
--- /dev/null
+++ b/shell/ash_test/ash-parsing/quote4.tests
@@ -0,0 +1,2 @@
+a_b='a b'
+echo "$a_b"