Merge multiple `listitem`s in `varlistentry`.

Docbook only allows a single `listitem` in a `varlistentry` so combine
multiple items into a single item.

[SVN r64831]

tools/quickbook

@@ -1 +1 @@
-Subproject commit aa694384400027f8fa426c60357397f05c70b50e
+Subproject commit 4b41d22c87b8a23f9a89d29be60bc4814863439f