Update DOMQuery::prepareInsert()

This change makes prepareInsert() return a DOMDocumentFragment
if the argument is a DOMQuery.

It allows append(), prepend(), and the other callers of
prepareInsert() to insert a DOMQuery that has multiple matches.
Update wrap(), wrapInner(), and wrapAll()

This makes these methods a bit more compatible with jQuery.
Merge pull request #128 from noisan/prepare-insert-method

Improve compatibility with jQuery